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Stockholders' Equity And Stock-Based Compensation (Schedule Of Fair Value Of Employee Stock Options) (Details)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Employee Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	70.00%	70.00%
Employee Stock Option [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years	6 years 1 month 6 days	4 months 24 days
Risk-free interest rate	0.40%	2.40%
Employee Stock Option [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years		6 years 1 month 6 days
Risk-free interest rate	1.70%	2.70%
2017 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility	70.00%	70.00%
2017 Employee Stock Purchase Plan [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years	6 months	6 months
Risk-free interest rate	0.90%	2.50%
2017 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term in years	1 year	1 year
Risk-free interest rate	1.00%	2.60%

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 7,864	$ 6,899
Investments	8,022	18,499
Prepaid expenses and other current assets	545	1,005
Total current assets	16,431	26,403
Property and equipment, net	2,633	2,566
Intangible assets, net	4,381	4,547
Goodwill	2,791	2,791
Right-of-use assets	5,043	5,114
Other asset	562	494
Total assets	31,841	41,915
Current liabilities:
Accounts payable	1,214	1,963
Accrued expenses	2,071	2,496
Lease liability, current	98
Total current liabilities	3,383	4,459
Lease liability, less current	6,690	6,719
Total liabilities	10,073	11,178
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $0.001 par value; authorized – 50,000 shares; no shares issued and outstanding
Common stock, $0.001 par value: authorized – 500,000 shares; issued and outstanding – 20,869 shares and 20,825 shares at March 31, 2020 and December 31, 2019, respectively	21	21
Additional paid-in-capital	156,291	153,401
Accumulated other comprehensive income	17	4
Accumulated deficit	(134,561)	(122,689)
Total stockholders' equity	21,768	30,737
Total liabilities and stockholders' equity	$ 31,841	$ 41,915

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net loss	$ (11,872)	$ (10,078)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	104	162
Amortization of intangible assets	166	167
Stock-based compensation	2,626	2,361
Net premium amortization and discount on available-for-sale securities	(4)	(96)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	460	229
Right-of-use assets	71
Other long-term assets	(68)	(107)
Accounts payable	(749)	(72)
Accrued expenses	(425)	98
Lease liabilities	69
Other current and non-current liabilities		6
Net cash used in operating activities	(9,622)	(7,330)
Cash flows from investing activities:
Purchases of property and equipment	(171)	(45)
Purchases of investments	(3,006)	(44,186)
Maturities of investments	13,500	8,500
Net cash provided by (used) in investing activities	10,323	(35,731)
Cash flows from financing activities:
Proceeds from issuance of common stock under employee stock purchase plan	255	272
Proceeds from exercises of stock options	9	222
Net cash provided by financing activities	264	494
Net increase (decrease) in cash	965	(42,567)
Cash and cash equivalents at beginning of period	6,899	51,103
Cash and cash equivalents at end of period	7,864	8,536
Supplemental disclosure of noncash investing and financing activities:
Change in unrealized gains on available-for-sale securities	$ 13	$ 3

Summary Of Significant Accounting Policies

3 Months Ended

Mar. 31, 2020

Summary Of Significant Accounting Policies [Abstract]

Summary Of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Going concern

As of March 31, 2020, the Company had an accumulated deficit of $134.6 million, cash outflows from operations of $9.6 million for the three months then ended, and cash, cash equivalents and investments of $15.9 million and anticipates that it may continue to incur significant operating losses for the next several years. Until such time as the Company can generate substantial product revenue and achieve profitability, the Company will need to raise additional capital. The Company plans to raise additional capital to fund its operations for at least the next twelve months from the date of issuance of the accompanying consolidated financial statements, including via a proposed rights offering that seek to raise gross proceeds of approximately $30 million, assuming such rights offering is fully subscribed and excluding the proceeds from any warrants which may be issued in the rights offering and exercised following the completion of the offering. There is no assurance that the rights offering will be successful, or that additional financing will be available when needed or that management of the Company will be able to obtain financing on terms acceptable to the Company. Accordingly, the Company’s management cannot conclude that such plans will be effectively implemented within twelve months from the date of issuance of the accompanying consolidated financial statements.

These factors, combined with the Company’s forecast of cash required to fund operations for a period of at least twelve months from the date of issuance of the accompanying consolidated financial statements, raise substantial doubt about the Company’s ability to continue as a going concern.

The accompanying consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The consolidated financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of this uncertainty.

COVID-19 Pandemic

The Company is subject to risks and uncertainties as a result of the novel coronavirus pandemic (COVID-19). The extent of the impact of the COVID-19 pandemic on the Company’s business is highly uncertain and difficult to predict, as the response to the pandemic is in its incipient stages and information is rapidly evolving. The Company considered the impact of COVID-19 on the assumptions and estimates used to determine the results reported and asset valuations as of March 31, 2020.

Basis of Presentation

The accompanying unaudited condensed consolidated financial statements have been prepared on a basis consistent with the Company’s December 31, 2019 audited Consolidated Financial Statements and include all adjustments, consisting of only normal recurring adjustments, necessary to fairly state the information set forth herein. The condensed consolidated financial statements have been prepared in accordance with the applicable rules and regulations of the Securities and Exchange Commission (SEC) and, as permitted by such rules and regulations, omit certain information and footnote disclosures necessary to present the financial statements in accordance with accounting principles generally accepted in the United States (U.S. GAAP). The condensed consolidated balance sheet as of December 31, 2019 was derived from the audited consolidated financial statements as of that date but does not include all of the information and footnotes required by U.S. GAAP for complete financial statements. These condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. The results of operations for the three-month period ended March 31, 2020 are not necessarily indicative of the results to be expected for the entire year or any future periods.

Principles of Consolidation

The accompanying condensed consolidated financial statements include the financial statements of Pulse Biosciences, Inc. and its wholly-owned subsidiaries. Intercompany balances and transactions, if any, have been eliminated in consolidation.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires the Company to make estimates and assumptions that affect the amounts reported in the Financial Statements and accompanying notes to the condensed consolidated financial statements. Estimates include, but are not limited to, the valuation of cash equivalents and investments, the valuation and recognition of share-based compensation and the useful lives assigned to long-lived assets. The Company evaluates its estimates and assumptions based on historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could differ materially from these estimates.

Significant Accounting Policies

There have been no material changes to the Company’s significant accounting policies during three-month period ended March 31, 2020, as compared to the significant accounting policies described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019.

Net Loss per Share

The Company calculates basic net loss per share by dividing net loss by the weighted-average number of shares of common stock outstanding during the period. Diluted net loss per share is computed by giving effect to all potential dilutive common stock equivalents outstanding during the period. For purposes of this calculation, options to purchase common stock and common stock warrants are considered common stock equivalents. Potential common shares that have an anti-dilutive effect (i.e., those that increase income per share or decrease loss per share) are excluded from the calculation of diluted net loss per share.

Basic and diluted net loss per common share is the same for all periods presented because all warrants, stock options and restricted stock units outstanding are anti-dilutive.

The following outstanding stock options, warrants and restricted stock units were excluded from the computation of diluted net loss per share for the periods presented because including them would have had an anti-dilutive effect:



	Three-Month Periods Ended
	March 31,
	2020		2019
Common stock warrants		167,847		213,485
Common stock options		3,891,607		2,871,770
Restricted stock units		222,606		222,606
Total		4,282,060		3,307,861

Recent Accounting Pronouncement

In December 2019, the Financial Accounting Standards Board issued Accounting Standards Update 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which eliminates certain exceptions related to the general principles in Accounting Standards Codification (ASC) 740 and makes amendments to other areas with the intention of simplifying various aspects related to accounting for income taxes. The new standard is effective for fiscal years beginning after December 15, 2020, including interim periods therein; with early adoption permitted. The Company is currently evaluating the impact that the standard will have on its financial statements and related disclosures; and does not expect the adoption to have a material impact on the Company’s financial statements.

Related Party Transactions	3 Months Ended
Related Party Transactions	Mar. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	9. Related Party Transactions Kenneth A. Clark, a director of the Company since November 2017, is a member of the law firm of Wilson Sonsini Goodrich and Rosati (WSGR), which also serves as the outside corporate counsel to the Company. During the three-month periods ended March 31, 2020 and 2019, the Company incurred expenses reported in general and administrative expenses in the consolidated statement of operations for legal services rendered by WSGR totaling approximately $0.1 million, respectively.

Fair Value Of Financial Instruments (Narrative) (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Fair Value Of Financial Instruments [Abstract]
Liabilities measured at fair value	$ 0	$ 0
Transfers between level 1, 2, or 3	$ 0

Summary Of Significant Accounting Policies (Anti-Dilutive Shares Excluded From Computation Of Diluted Net Loss Per Share) (Details) - shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	4,282,060	3,307,861
Warrants to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	167,847	213,485
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	3,891,607	2,871,770
Restricted Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total	222,606	222,606

Fair Value Of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2020

Fair Value Of Financial Instruments [Abstract]

Fair Value Of Financial Assets Measured On A Recurring Basis


		March 31, 2020								December 31, 2019
Assets	Classification		Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Money market funds	Cash and cash equivalents	$	6,989		—		—	$	6,989	$	6,429	$	—	$	—	$	6,429
U.S. Treasury Securities	Investments		—		8,022		—		8,022		—		18,499		—		18,499
Total assets measured at fair value		$	6,989	$	8,022	$	—	$	15,011	$	6,429	$	18,499	$	—	$	24,928

Research Grants And Agreements	3 Months Ended
Research Grants And Agreements	Mar. 31, 2020
Research Grants And Agreements [Abstract]
Research Grants And Agreements	7. Research Grants and Agreements Sponsored Research Agreement The Company may annually sponsor research activities (SRAs) performed by Old Dominion University’s Frank Reidy Center (ODURF). ODURF is compensated by the Company for its conduct of each study in accordance with the budget and payment terms set forth in the applicable task order. During the year ended December 31, 2019, the Company agreed to sponsor $0.8 million in research during the subsequent 12-month period funded through monthly payments made upon ODURF certifying, to the Company’s reasonable satisfaction, that ODURF has met its obligations pursuant to the specified task order and statement of work. The principal investigator may transfer funds with the budget as needed without the Company’s approval so long as the obligations of ODURF under the task order and statement of work remain unchanged and unimpaired. As of March 31, 2020, approximately $0.4 million remained payable under this agreement. During the three-month periods ended March 31, 2020 and 2019, the Company paid and incurred costs related to the SRAs equal to $0.2 million, respectively.

Commitments And Contingencies (Tables)

3 Months Ended

Mar. 31, 2020

Commitments And Contingencies [Abstract]

Schedule Of Future Minimum Lease Payments


Year Ending December 31:
2020 (remaining 9 months)	$	549
2021		986
2022		1,071
2023		1,094
2024		1,133
2025		1,172
Thereafter		4,885
Total lease payments		10,890
Less imputed interest		(4,102)
Total lease liabilities	$	6,788

Schedule Of Information Related To Right-Of-Use Assets And Lease Liabilities


Other supplemental non-cash information:
Cash paid for operating lease liabilities	$	377
Operating lease liabilities arising from ROU assets		5,027

Current operating lease liabilities		98
Non-current operating lease liabilities		6,690
Total lease liabilities	$	6,788

Weighted average remaining lease term		9.59 years
Weighted average discount rate		10%

Commitments And Contingencies

3 Months Ended

Mar. 31, 2020

Commitments And Contingencies [Abstract]

Commitments And Contingencies

8. Commitments and Contingencies

Operating Leases

During January 2017, the Company entered into a five-year lease (the Existing Lease) for approximately 15,700 square feet for its corporate headquarters located in Hayward, California (the Existing Premises). The lease commenced during July 2017.

During May 2019, the Company entered into Lease Amendment 1 (the Amendment) in relation to the Existing Lease and added the lease of new premises of approximately 34,600 square feet (Expansion Premises); additionally, the term of the Existing Lease was extended to October 2029.

The Company evaluated the Amendment under the provisions of ASC 842 that it adopted on January 1, 2019, and accounted the Amendment as a single contract with the Existing Lease because the additional lease payments due to the Amendment was not commensurate with the right-of-use (ROU) asset granted to the Company. Though the Amendment was accounted for as a single contract, the Existing Premises and Expansion Premises are accounted for as separate lease components. Accordingly, the Company measured and allocated consideration to each lease component as of the modification date. Upon commencement of each lease component, the Company will reassess and calculate the lease liability and ROU asset for the respective component.

Information related to the Company’s ROU assets and related lease liabilities were as follows (in thousands except for remaining lease term and discount rate):


Year Ending December 31:
2020 (remaining 9 months)	$	549
2021		986
2022		1,071
2023		1,094
2024		1,133
2025		1,172
Thereafter		4,885
Total lease payments		10,890
Less imputed interest		(4,102)
Total lease liabilities	$	6,788


Other supplemental non-cash information:
Cash paid for operating lease liabilities	$	377
Operating lease liabilities arising from ROU assets		5,027

Current operating lease liabilities		98
Non-current operating lease liabilities		6,690
Total lease liabilities	$	6,788

Weighted average remaining lease term		9.59 years
Weighted average discount rate		10%

During the three-month periods ended March 31, 2020 and 2019, rent expense, including common area maintenance charges, was approximately $0.2 million and $0.1 million, respectively.

Legal Proceedings

The Company maintains indemnification agreements with its directors and officers that may require the Company to indemnify them against liabilities that arise by reason of their status or service as directors or officers, except as prohibited by applicable law.

From time to time, the Company may be involved in a variety of claims, lawsuits, investigations and proceedings relating to securities laws, product liability, patent infringement, contract disputes and other matters relating to various claims that arise in the normal course of the Company’s business. The Company currently believes that these ordinary course matters are not material to the condensed consolidated financial statements of the business; however, the results of litigation and claims are inherently unpredictable.

Commitments And Contingencies (Schedule Of Information Related To Right-Of-Use Assets And Lease Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Commitments And Contingencies [Abstract]
Cash paid for operating lease liabilities	$ 377
Operating lease liabilities arising from ROU assets including impact of ASC 842 adoption	5,027
Current operating lease liabilities	98
Non-current operating lease liabilities	6,690	$ 6,719
Total lease liabilities	$ 6,788
Weighted average remaining lease term	3 years 8 months 1 day
Weighted average discount rate	10.00%

Stockholders' Equity And Stock-Based Compensation (Schedule Of Stock-Based Compensation Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,626	$ 2,361
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,749	1,485
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 877	$ 876

Document And Entity Information - shares	3 Months Ended
Document And Entity Information - shares	Mar. 31, 2020	May 04, 2020
Document And Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-34899
Entity Registrant Name	Pulse Biosciences, Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	46-5696597
Entity Address, Address Line One	3957 Point Eden Way
Entity Address, City or Town	Hayward
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94545
City Area Code	510
Local Phone Number	906-4600
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	PLSE
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		20,869,443
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Entity Central Index Key	0001625101
Amendment Flag	false

Goodwill (Narrative) (Details)	3 Months Ended	12 Months Ended
Goodwill (Narrative) (Details)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2014 USD ($) entity
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Number of purchased companies \| entity			3
Goodwill	$ 2,791,000	$ 2,791,000	$ 2,800,000
Goodwill impairment	$ 0	$ 0
TPI, BEM And NB [Member]
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Aggregate consideration			$ 5,500,000

Stockholders' Equity And Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2020

Stockholders' Equity [Line Items]

Summary Of Stock Option Activity


	Stock Options Outstanding
			Weighted
	Number		average
	of shares		exercise price
Balances — December 31, 2019	3,749,186	$	16.18
Options granted	178,000
Options exercised	(750)
Options canceled	(12,855)
Options expired	(21,974)
Balances — March 31, 2020	3,891,607	$	15.67
Exercisable — March 31, 2020	2,301,566	$	16.48

Summary Of Stock-Based Compensation Expense



	Three-Month Periods Ended
	March 31,
	2020		2019
General and administrative	$	1,749	$	1,485
Research and development		877		876
Total stock-based compensation expense	$	2,626	$	2,361

Employee Stock Option [Member]

Stockholders' Equity [Line Items]

Schedule Of Fair Value Of Employee Stock Options


	Three-Month Periods Ended March 31,
	2020	2019
Expected term in years	6.1	0.4 - 6.1
Expected volatility	70%	70%
Risk-free interest rate	0.4% - 1.7%	2.4% - 2.7%
Dividend yield	—	—

2017 Employee Stock Purchase Plan [Member]

Stockholders' Equity [Line Items]

Schedule Of Fair Value Of Employee Stock Options


	Three-Month Periods Ended March 31,
	2020	2019
Expected term in years	0.5 - 1.0	0.5 - 1.0
Expected volatility	70%	70%
Risk-free interest rate	0.9% - 1.0%	2.5% - 2.6%
Dividend yield	—	—

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2020	Dec. 31, 2019
Condensed Consolidated Balance Sheets [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	50,000,000	50,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	20,869,000	20,825,000
Common stock, shares outstanding	20,869,000	20,825,000

Description Of The Business	3 Months Ended
Description Of The Business	Mar. 31, 2020
Description Of The Business [Abstract]
Description Of The Business	1. Description of the Business Pulse Biosciences, Inc. (together with its subsidiaries, the Company) is a novel bioelectric medicine company committed to health innovation that improves and potentially extends the lives of patients. The Company is pursuing regulatory clearance to market its first product, its proprietary CellFX® System. The Company’s CellFX System utilizes its patented Nano-Pulse Stimulation™ (NPS™) technology to treat a variety of applications for which an optimal solution remains unfulfilled. NPS is a proprietary technology that delivers nano-second duration pulses of high amplitude electrical energy to non-thermally clear targeted cells while sparing adjacent non-cellular tissue. The cell-specific effects of NPS technology have been validated in a series of completed and ongoing clinical studies. The Company was incorporated in Nevada on May 19, 2014. On June 18, 2018, the Company reincorporated from the State of Nevada to the State of Delaware. The Company’s headquarters and manufacturing and research facility are located in Hayward, California. The Company’s activities are subject to significant risks and uncertainties, including the need for additional capital. The Company has not yet commenced any revenue-generating operations, does not have any cash flows from operations, and will need to raise additional capital to finance its operations. However, there can be no assurances that the Company will be able to obtain additional financing on acceptable terms and in the amounts necessary to fully fund its operating requirements. Pulse Biosciences, CellFX, Nano-Pulse Stimulation, and NPS and the stylized logos are trademarks or registered trademarks of the Company in the United States and other countries.

Commitments And Contingencies (Schedule Of Future Minimum Lease Payments) (Details) $ in Thousands	Mar. 31, 2020 USD ($)
Commitments And Contingencies [Abstract]
2020 (remaining 9 months)	$ 549
2021	986
2022	1,071
2023	1,094
2024	1,133
2025	1,172
Thereafter	4,885
Total lease payments	10,890
Less imputed interest	(4,102)
Total lease liabilities	$ 6,788

Fair Value Of Financial Instruments (Fair Value Of Financial Assets Measured On A Recurring Basis) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
ASSETS
Total assets measured at fair value	$ 15,011	$ 24,928
Cash and cash equivalents [Member] \| Money market funds [Member]
ASSETS
Total cash and cash equivalents	6,989	6,429
Investments [Member] \| U.S. Treasury Securities [Member]
ASSETS
Total investments	8,022	18,499
Level 1 [Member]
ASSETS
Total assets measured at fair value	6,989	6,429
Level 1 [Member] \| Cash and cash equivalents [Member] \| Money market funds [Member]
ASSETS
Total cash and cash equivalents	6,989	6,429
Level 2 [Member]
ASSETS
Total assets measured at fair value	8,022	18,499
Level 2 [Member] \| Investments [Member] \| U.S. Treasury Securities [Member]
ASSETS
Total investments	$ 8,022	$ 18,499

Stockholders' Equity And Stock-Based Compensation (Summary Of Stock Option Activity) (Details) - Employee Stock Option [Member]	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Beginning Balance, Number of shares \| shares	3,749,186
Options granted, Number of shares \| shares	178,000
Options exercised, Number of shares \| shares	(750)
Options canceled, Number of shares \| shares	(12,855)
Options expired, Number of shares \| shares	(21,974)
Ending Balance, Number of shares \| shares	3,891,607
Exercisable, Number of shares \| shares	2,301,566
Beginning Balance, Weighted average exercise price per share \| $ / shares	$ 16.18
Options granted, Weighted average exercise price per share \| $ / shares
Options exercised, Weighted average exercise price per share \| $ / shares
Options canceled, Weighted average exercise price per share \| $ / shares
Options expired, Weighted average exercise price per share \| $ / shares
Ending Balance, Weighted average exercise price per share \| $ / shares	15.67
Exercisable, Weighted average exercise price per share \| $ / shares	$ 16.48

Summary Of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2020

Summary Of Significant Accounting Policies [Abstract]

Anti-Dilutive Shares Excluded From Computation Of Diluted Net Loss Per Share



	Three-Month Periods Ended
	March 31,
	2020		2019
Common stock warrants		167,847		213,485
Common stock options		3,891,607		2,871,770
Restricted stock units		222,606		222,606
Total		4,282,060		3,307,861

Balance Sheet Components (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Balance Sheet Components [Abstract]
Depreciation expense	$ 104	$ 162
Intangible asset useful life	12 years
Compensation expense	$ 1,172		$ 1,699

Summary Of Significant Accounting Policies (Policy)

3 Months Ended

Mar. 31, 2020

Summary Of Significant Accounting Policies [Abstract]

Going Concern

Going concern

COVID-19 Pandemic

Basis Of Presentation

Basis of Presentation

Principles Of Consolidation

Principles of Consolidation

Use Of Estimates

Use of Estimates

Significant Accounting Policies

Net Loss Per Share

Net Loss per Share

Basic and diluted net loss per common share is the same for all periods presented because all warrants, stock options and restricted stock units outstanding are anti-dilutive.



	Three-Month Periods Ended
	March 31,
	2020		2019
Common stock warrants		167,847		213,485
Common stock options		3,891,607		2,871,770
Restricted stock units		222,606		222,606
Total		4,282,060		3,307,861

Recent Accounting Pronouncements

Recent Accounting Pronouncement

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Summary Of Significant Accounting Policies [Abstract]
Accumulated deficit	$ (134,561)	$ (122,689)
Cash, cash equivalents, and investments	15,900
Right-of-use assets	$ 5,043	$ 5,114

Condensed Consolidated Statements Of Operations And Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Condensed Consolidated Statements Of Operations And Comprehensive Loss [Abstract]
Revenue
Operating expenses:
General and administrative	5,603	4,401
Research and development	6,181	5,842
Amortization of intangible assets	166	167
Total operating expenses	11,950	10,410
Other income:
Interest income	78	332
Total other income	78	332
Net loss	(11,872)	(10,078)
Other comprehensive loss:
Unrealized gain on available-for-sale securities	13	3
Comprehensive loss	$ (11,859)	$ (10,075)
Net loss per share:
Basic and diluted net loss per share	$ (0.57)	$ (0.49)
Weighted average shares used to compute net loss per common share - basic and diluted	20,838	20,679

Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2020

Balance Sheet Components [Abstract]

Schedule Of Property And Equipment, Net



	March 31,		December 31,
	2020		2019
Leasehold improvements	$	2,248	$	2,248
Laboratory equipment		677		677
Furniture, fixtures, and equipment		466		466
Software		118		118
Construction in progress		714		543
		4,223		4,052
Less: Accumulated depreciation		(1,590)		(1,486)
	$	2,633	$	2,566

Schedule Of Intangible Assets, Net



	March 31,		December 31,
	2020		2019
Acquired patents and licenses	$	7,985	$	7,985
Less: Accumulated amortization		(3,604)		(3,438)
	$	4,381	$	4,547

Schedule Of Amortization Of Intangible Assets


Year Ending December 31:
2020 (remaining 9 months)	$	499
2021		665
2022		665
2023		665
2024		665
2025		665
Thereafter		557
	$	4,381

Schedule Of Accrued Expenses



	March 31,		December 31,
	2020		2019
Compensation expense	$	1,172	$	1,699
Accrued clinical		512		262
Professional fees		37		51
Property and equipment		234		234
Other		116		250
	$	2,071	$	2,496

Balance Sheet Components (Schedule Of Intangible Assets, Net) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Balance Sheet Components [Abstract]
Acquired patents and licenses	$ 7,985	$ 7,985
Less: Accumulated amortization	(3,604)	(3,438)
Intangible assets, net	$ 4,381	$ 4,547

Fair Value Of Financial Instruments

3 Months Ended

Mar. 31, 2020

Fair Value Of Financial Instruments [Abstract]

Fair Value Of Financial Instruments

3. Fair Value of Financial Instruments

The authoritative guidance with respect to fair value established a fair value hierarchy that prioritizes the inputs to valuation techniques used to measure fair value into three levels, and requires that assets and liabilities carried at fair value to be classified and disclosed in one of three categories, as presented below.

Level 1 - Observable inputs such as quoted prices in active markets for an identical asset or liability that the Company has the ability to access as of the measurement date. Financial assets and liabilities utilizing Level 1 inputs include money market funds.

Level 2 - Inputs, other than quoted prices included within Level 1, which are directly observable for the asset or liability or indirectly observable through corroboration with observable market data. Financial assets and liabilities utilizing Level 2 inputs include commercial paper, corporate bonds, and asset-backed securities.

Level 3 - Unobservable inputs for which there is little or no market data for the asset or liability which requires the reporting entity to develop its own assumptions. The Company did not classify any of its investments within Level 3 of the fair value hierarchy.

The following table sets forth the fair value of the Company’s financial assets measured on a recurring basis as of March 31, 2020 and December 31, 2019, respectively (in thousands):


		March 31, 2020								December 31, 2019
Assets	Classification		Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3		Total
Money market funds	Cash and cash equivalents	$	6,989		—		—	$	6,989	$	6,429	$	—	$	—	$	6,429
U.S. Treasury Securities	Investments		—		8,022		—		8,022		—		18,499		—		18,499
Total assets measured at fair value		$	6,989	$	8,022	$	—	$	15,011	$	6,429	$	18,499	$	—	$	24,928

The Company did not have any financial liabilities measured on a recurring basis as of March 31, 2020 or December 31, 2019.

During the three-month period ended March 31, 2020, there were no transfers between Level 1, Level 2 or Level 3 assets or liabilities reported at fair value on a recurring basis, and the valuation techniques used did not change compared to the Company’s established practice.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Goodwill	3 Months Ended
Goodwill	Mar. 31, 2020
Goodwill [Abstract]
Goodwill	5. Goodwill In 2014, the Company acquired three companies (the acquisitions) for aggregate consideration of $5.5 million. In accordance with ASC Topic 805, Business Combinations, the Company recorded goodwill of $2.8 million in connection with the acquisitions as the consideration paid exceeded the fair value of the net tangible assets and the intangible assets acquired. The Company reviews goodwill for impairment at least annually or whenever changes in circumstances indicate that the carrying amount of goodwill may not be recoverable. Based on the Company’s annual impairment test as of December 31, 2019 the Company determined that no impairment of goodwill existed and was not aware of any indicators of impairment at such date. In addition, there were no indicators of impairment at March 31, 2020.

Balance Sheet Components (Schedule Of Amortization Of Intangible Assets) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Balance Sheet Components [Abstract]
2020 (remaining 9 months)	$ 499
2021	665
2022	665
2023	665
2024	665
2025	665
Thereafter	557
Intangible assets, net	$ 4,381	$ 4,547

Balance Sheet Components (Schedule Of Property And Equipment, Net) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Equipment, gross	$ 4,223	$ 4,052
Less: Accumulated depreciation and amortization	(1,590)	(1,486)
Equipment, net	2,633	2,566
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Equipment, gross	2,248	2,248
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Equipment, gross	677	677
Furniture, Fixtures, And Equipment [Member]
Property, Plant and Equipment [Line Items]
Equipment, gross	466	466
Software [Member]
Property, Plant and Equipment [Line Items]
Equipment, gross	118	118
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Equipment, gross	$ 714	$ 543

Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]	Total
Balance at Dec. 31, 2018	$ 21	$ 142,032	$ (1)	$ (75,718)	$ 66,334
Balance, shares at Dec. 31, 2018	20,593
Issuance of shares upon exercise of stock options		272			272
Issuance of shares upon exercise of stock options, shares	99
Issuance of shares under employee stock purchase plan		222			222
Issuance of shares under employee stock purchase plan, shares	18
Stock-based compensation expense		2,361			2,361
Unrealized gain on available-for-sale securities			3		3
Net loss				(10,078)	(10,078)
Balance at Mar. 31, 2019	$ 21	144,887	2	(85,796)	59,114
Balance, shares at Mar. 31, 2019	20,710
Balance at Dec. 31, 2019	$ 21	153,401	4	(122,689)	$ 30,737
Balance, shares at Dec. 31, 2019	20,825				20,825
Issuance of shares upon exercise of stock options		9			$ 9
Issuance of shares upon exercise of stock options, shares	1
Issuance of shares under employee stock purchase plan		255			255
Issuance of shares under employee stock purchase plan, shares	43
Stock-based compensation expense		2,626			2,626
Unrealized gain on available-for-sale securities			13		13
Net loss				(11,872)	(11,872)
Balance at Mar. 31, 2020	$ 21	$ 156,291	$ 17	$ (134,561)	$ 21,768
Balance, shares at Mar. 31, 2020	20,869				20,869

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Related Party Transactions (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Wilson Sonsini Goodrich And Rosati (WSGR) [Member]
Related Party Transaction [Line Items]
Related party expenses	$ 0.1	$ 0.1

Stockholders' Equity And Stock-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		6 Months Ended
	Jan. 01, 2020	Mar. 31, 2020	Mar. 31, 2019	Jun. 30, 2018	Apr. 06, 2020	Dec. 31, 2019	Nov. 30, 2017	Dec. 31, 2016	Dec. 31, 2014
Stockholders' Equity [Line Items]
Common stock, par value		$ 0.001				$ 0.001
Proceeds from issuance of common stock under employee stock purchase plan		$ 255	$ 272
Common stock, shares issued		20,869,000				20,825,000
Total stock-based compensation expense		$ 2,626	2,361
Cash received from option exercises		$ 9	222
2017 Employee Stock Purchase Plan [Member]
Stockholders' Equity [Line Items]
Common stock, shares issued		43,224
Shares authorized		250,000
Increase in shares available for issuance threshold of common stock outstanding, number of shares		450,000
Increase in shares available for issuance threshold of common stock outstanding, percent outstanding		1.50%
Shares available for grant		396,971
2017 Inducement Equity Incentive Plan [Member]
Stockholders' Equity [Line Items]
Term period		10 years
Shares authorized							1,000,000
Shares available for grant		8,492
2017 Plan [Member]
Stockholders' Equity [Line Items]
Term period		10 years
Shares authorized		1,500,000
Additional common stock reserved for issuance	833,018
Increase in shares available for issuance threshold of common stock outstanding, number of shares		1,200,000
Increase in shares available for issuance threshold of common stock outstanding, percent outstanding		4.00%
Shares available for grant		1,721,093
First Vesting Portion [Member] \| 2017 Inducement Equity Incentive Plan [Member]
Stockholders' Equity [Line Items]
Vesting percentage		25.00%
General and administrative [Member]
Stockholders' Equity [Line Items]
Total stock-based compensation expense		$ 1,749	1,485
Research and development [Member]
Stockholders' Equity [Line Items]
Total stock-based compensation expense		$ 877	$ 876
Employee Stock Option [Member]
Stockholders' Equity [Line Items]
Options granted		178,000
Warrants exercised		750
Exercise price		$ 16.48
Performance Shares [Member]
Stockholders' Equity [Line Items]
Options granted				69,375
Subsequent Event [Member]
Stockholders' Equity [Line Items]
Value of warrants/rights					$ 30,000
Private Placement [Member]
Stockholders' Equity [Line Items]
Common stock, par value									$ 0.001
Common Stock
Stockholders' Equity [Line Items]
Warrants exercised		1,000	99,000
MDB Capital Group, LLC [Member] \| Initial Public Offering [Member]
Stockholders' Equity [Line Items]
Price per share								$ 5.00
Warrants/rights outstanding		121,609
Exercisable period of warrants or rights		5 years
Number of common shares called by issuance of warrants								574,985
MDB Capital Group, LLC [Member] \| Private Placement [Member]
Stockholders' Equity [Line Items]
Price per share									$ 2.67
Warrants/rights outstanding		46,238
Exercisable period of warrants or rights		7 years
Number of common shares called by issuance of warrants									299,625

Research Grants And Agreements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense	$ 6,181	$ 5,842
Sponsored Research Agreement ("SRA") [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense	$ 200	$ 200
ODURF [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Period of time for Sponsored Research Agreement ("SRA")	12 months
ODURF [Member] \| Sponsored Research Agreement ("SRA") [Member]
Research and Development Arrangement, Contract to Perform for Others [Line Items]
Research and development expense	$ 800
Remaining sponsorship	$ 400

Balance Sheet Components

3 Months Ended

Mar. 31, 2020

Balance Sheet Components [Abstract]

Balance Sheet Components

4. Balance Sheet Components

Property and Equipment, net

Property and equipment, net consisted of the following (in thousands):



	March 31,		December 31,
	2020		2019
Leasehold improvements	$	2,248	$	2,248
Laboratory equipment		677		677
Furniture, fixtures, and equipment		466		466
Software		118		118
Construction in progress		714		543
		4,223		4,052
Less: Accumulated depreciation		(1,590)		(1,486)
	$	2,633	$	2,566

Depreciation expense was $0.1 million for the three-month periods ended March 31, 2020 and 2019, respectively.

Intangible Assets, Net

Intangible assets primarily consist of acquired licenses to utilize certain patents, know-how and technology relating to the Company’s NPS for biomedical applications acquired from Old Dominion University Research Foundation (ODURF), Eastern Virginia Medical School, and the University of Southern California. In addition, the Company entered into a Sponsored Research Agreement with Old Dominion University’s Frank Reidy Research Center for Bioelectrics, which includes certain intellectual property rights arising from the research. The Company is amortizing the intangible assets over an estimated useful life of 12 years.

Intangible assets, net consisted of the following (in thousands):



	March 31,		December 31,
	2020		2019
Acquired patents and licenses	$	7,985	$	7,985
Less: Accumulated amortization		(3,604)		(3,438)
	$	4,381	$	4,547

A schedule of the amortization of intangible assets for the remainder of 2020 and the succeeding five fiscal years and thereafter is as follows (in thousands):


Year Ending December 31:
2020 (remaining 9 months)	$	499
2021		665
2022		665
2023		665
2024		665
2025		665
Thereafter		557
	$	4,381

Accrued Expenses

Accrued expenses consisted of the following (in thousands):



	March 31,		December 31,
	2020		2019
Compensation expense	$	1,172	$	1,699
Accrued clinical		512		262
Professional fees		37		51
Property and equipment		234		234
Other		116		250
	$	2,071	$	2,496

Commitments And Contingencies (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	May 31, 2019 ft²	Jan. 31, 2017 ft²
Commitments and Contingencies [Line Items]
Rent expense, including common area maintenance charges \| $	$ 0.2	$ 0.1
Hayward, CA [Member]
Commitments and Contingencies [Line Items]
Lease term	5 years
Area Of Lease				15,700
Lease Amendment [Member]
Commitments and Contingencies [Line Items]
Area Of Lease			34,600

Balance Sheet Components (Schedule Of Accrued Expenses) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Balance Sheet Components [Abstract]
Compensation expense	$ 1,172	$ 1,699
Accrued clinical	512	262
Professional fees	37	51
Property and equipment	234	234
Other	116	250
Accrued expenses	$ 2,071	$ 2,496

Stockholders' Equity And Stock-Based Compensation

3 Months Ended

Mar. 31, 2020

Stockholders' Equity And Stock-Based Compensation [Abstract]

Stockholders' Equity And Stock-Based Compensation

6. Stockholders’ Equity and Stock-Based Compensation

Common Stock Warrants

In connection with a private placement of the Company’s common stock, par value $0.001 per share, in 2014, the Company issued warrants as compensation to the placement agent to purchase a total of 299,625 shares of its common stock at a price of $2.67 per share (the Private Placement Warrants). The Private Placement Warrants are exercisable for period of seven years from issuance. As of March 31, 2020, a total of 46,238 of Private Placement Warrants were outstanding. In connection with the closing of the Company’s initial public offering in 2016, the Company issued warrants as compensation to its underwriters to purchase a total of 574,985 shares of its common stock at a price of $5.00 per share (the IPO Warrants). The IPO Warrants are exercisable for a period of five years from issuance. As of March 31, 2020, a total of 121,609 of the IPO Warrants were outstanding.

Equity Plans

2017 Equity Incentive Plan and 2017 Inducement Equity Incentive Plan

The Board of Directors of the Company (the Board) previously adopted, and the Company’s stockholders approved, the Company’s 2017 Equity Incentive Plan (the 2017 Plan).

The 2017 Plan has a 10-year term, and provides for the grant of stock options, stock appreciation rights, restricted stock, restricted stock units, performance units, and performance shares to employees, directors and consultants of the Company and any parent or subsidiary of the Company, as the Compensation Committee of the Board may determine. Subject to an annual evergreen increase and adjustment in the case of certain capitalization events, the Company initially reserved 1,500,000 shares of the Company’s common stock for issuance pursuant to awards under the 2017 Plan. In addition, shares remaining available under the Company’s 2015 Equity Incentive Plan, as amended (the 2015 Plan), and shares reserved but not issued pursuant to outstanding equity awards that expire or terminate without being exercised or that are forfeited or repurchased by the Company will be added to the shares of common stock available for issuance under the 2017 Plan. The 2017 Plan is administered by the Board’s Compensation Committee. Effective January 1, 2020, the Company’s Board authorized an increase in the number of shares of common stock available under the 2017 Plan increased by 833,018 shares pursuant to the evergreen provision of the 2017 Plan. Pursuant to the 2017 Plan, the 2019 share increase is determined based on the least of (i) 1,200,000 shares, (ii) 4% of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Board. As of March 31, 2020, 1,721,093 shares of common stock remained available for issuance under the 2017 Plan.

During November 2017, the Board adopted the 2017 Inducement Equity Incentive Plan (the Inducement Plan) and reserved 1,000,000 shares of the Company’s common stock for issuance pursuant to equity awards granted under the Inducement Plan. The Inducement Plan was adopted without stockholder approval.

The Inducement Plan has a 10-year term, and provides for the grant of equity-based awards, including nonstatutory stock options, restricted stock units, restricted stock, stock appreciation rights, performance shares and performance units, and its terms are substantially similar to the 2017 Plan, including with respect to treatment of equity awards in the event of a “merger” or “change in control” as defined under the Inducement Plan. Options issued under the Inducement Plan may have a term up to ten years and have variable vesting provisions. New hire grants generally vest 25% annual starting upon the first anniversary of the grant. Equity-based awards issued under the Inducement Plan are only issuable to individuals not previously engaged as employees or non-employee directors of the Company prior to the Inducement Plan’s adoption date. As of March 31, 2020, 8,492 shares of common stock remained available for issuance under the Inducement Plan.

Certain stock options awarded to the Company’s executives contain performance conditions related to certain financial measures and achievements of strategic/operational milestones (performance options). As of March 31, 2020, it is not probable that these performance conditions will be achieved and accordingly no stock compensation has been recorded for these performance options to date.

2017 Employee Stock Purchase Plan

The Board previously adopted and the stockholders approved the Company’s 2017 Employee Stock Purchase Plan (the 2017 ESPP).

The 2017 ESPP is a broad-based plan that provides employees of the Company and its designated affiliates with the opportunity to become stockholders through periodic payroll deductions that are applied towards the purchase of Company common shares at a discount from the then-current market price. Subject to adjustment in the case of certain capitalization events, a total of 250,000 common shares of the Company were available for purchase at adoption of the 2017 ESPP. Pursuant to the 2017 ESPP, the annual share increase pursuant to the evergreen provision is determined based on the least of (i) 450,000 shares, (ii) 1.5% of the Company’s common stock outstanding at December 31 of the immediately preceding year, or (iii) such number of shares as determined by the Board. During January 2019, the Board determined not to increase the number of shares of common stock available under the 2017 ESPP pursuant to the evergreen provision of the 2017 ESPP. During the three-month period ended March 31, 2020, the Company issued 43,224 shares of common stock under the 2017 ESPP. As of March 31, 2020, 396,971 shares of common stock remained available for issuance under the 2017 ESPP.

A summary of stock option activity under the 2015 Plan, 2017 Plan and Inducement Plan for the three-month period ended March 31, 2020 is presented below:


	Stock Options Outstanding
			Weighted
	Number		average
	of shares		exercise price
Balances — December 31, 2019	3,749,186	$	16.18
Options granted	178,000
Options exercised	(750)
Options canceled	(12,855)
Options expired	(21,974)
Balances — March 31, 2020	3,891,607	$	15.67
Exercisable — March 31, 2020	2,301,566	$	16.48

The table above excludes 69,375 performance stock options granted for which the performance criteria had not been established as of March 31, 2020.

Stock-based Compensation

Total stock-based compensation expense consisted of the following (in thousands):



	Three-Month Periods Ended
	March 31,
	2020		2019
General and administrative	$	1,749	$	1,485
Research and development		877		876
Total stock-based compensation expense	$	2,626	$	2,361

The Company estimated the fair value of employee stock options on the grant date using the Black-Scholes option pricing model. The estimated fair value of employee stock options is amortized on a straight-line basis over the requisite service period of the awards. The Company reviews and, when deemed appropriate, updates the assumptions used on a periodic basis. Due to the limited trading history of the Company’s common stock, the Company utilizes a portfolio of comparable companies to estimate volatility. The fair value of employee stock options was estimated using the following weighted-average assumptions:


	Three-Month Periods Ended March 31,
	2020	2019
Expected term in years	6.1	0.4 - 6.1
Expected volatility	70%	70%
Risk-free interest rate	0.4% - 1.7%	2.4% - 2.7%
Dividend yield	—	—

The Company estimated the fair value of ESPP on the grant date using the Black-Scholes option pricing model. The estimated fair value of ESPP is amortized on a straight-line basis over the requisite service period of the awards. The Company reviews and, when deemed appropriate, updates the assumptions used on a periodic basis. The Company utilizes its estimated volatility in the Black-Scholes option pricing model to determine the fair value of ESPP. The fair value of ESPP was estimated using the following weighted-average assumptions:


	Three-Month Periods Ended March 31,
	2020	2019
Expected term in years	0.5 - 1.0	0.5 - 1.0
Expected volatility	70%	70%
Risk-free interest rate	0.9% - 1.0%	2.5% - 2.6%
Dividend yield	—	—

The fair value of restricted stock unit (RSUs) awards is determined based on the number of units granted and the closing price of the Company’s common stock as of the grant date. The estimated fair value of RSUs is recognized on a straight-line basis over the requisite service period.