STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Revision of Prior Period, Accounting Standards Update, Adjustment	Follow-on Offering	Common Stock	Common Stock Follow-on Offering	Additional Paid-In Capital	Additional Paid-In Capital Follow-on Offering	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit	Accumulated Deficit Revision of Prior Period, Accounting Standards Update, Adjustment
Beginning balance (in shares) at Dec. 31, 2018				23,401,675
Beginning balance at Dec. 31, 2018	$ 163,999			$ 23		$ 310,941		$ (52)	$ (146,913)
Stockholders' Equity [Roll Forward]
Stock options exercised (in shares)				100,089
Stock options exercised	166			$ 1		165
Issuance of common stock (in shares)				1,246
Issuance of common stock	58					58
Stock-based compensation expense	1,391					1,391
Other comprehensive income (loss)	68							68
Net loss	(8,266)								(8,266)
Ending balance (in shares) at Mar. 31, 2019				23,503,010
Ending balance at Mar. 31, 2019	157,416			$ 24		312,555		16	(155,179)
Beginning balance (in shares) at Dec. 31, 2018				23,401,675
Beginning balance at Dec. 31, 2018	$ 163,999			$ 23		310,941		(52)	(146,913)
Ending balance (in shares) at Dec. 31, 2019	24,107,350			24,107,350
Ending balance at Dec. 31, 2019	$ 139,835	$ 12		$ 24		319,865		102	(180,156)	$ 12
Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Beginning balance (in shares) at Mar. 31, 2019				23,503,010
Beginning balance at Mar. 31, 2019	$ 157,416			$ 24		312,555		16	(155,179)
Stockholders' Equity [Roll Forward]
Stock options exercised (in shares)				378,490
Stock options exercised	604					604
Issuance of common stock (in shares)				1,043
Issuance of common stock	58					58
Issuance of common stock for employee stock purchase plan (in shares)				18,187
Issuance of common stock for employee stock purchase plan	637					637
Stock-based compensation expense	1,389					1,389
Other comprehensive income (loss)	35							35
Net loss	(7,650)								(7,650)
Ending balance (in shares) at Jun. 30, 2019				23,900,730
Ending balance at Jun. 30, 2019	$ 152,489			$ 24		315,243		51	(162,829)
Beginning balance (in shares) at Dec. 31, 2019	24,107,350			24,107,350
Beginning balance at Dec. 31, 2019	$ 139,835	12		$ 24		319,865		102	(180,156)	12
Stockholders' Equity [Roll Forward]
Stock options exercised (in shares)				254,142
Stock options exercised	787					787
Issuance of common stock (in shares)				897
Issuance of common stock	72					72
Stock-based compensation expense	2,749					2,749
Other comprehensive income (loss)	193							193
Net loss	(16,245)								(16,245)
Ending balance (in shares) at Mar. 31, 2020				24,362,389
Ending balance at Mar. 31, 2020	$ 127,403			$ 24		323,473		295	(196,389)
Beginning balance (in shares) at Dec. 31, 2019	24,107,350			24,107,350
Beginning balance at Dec. 31, 2019	$ 139,835	$ 12		$ 24		319,865		102	(180,156)	$ 12
Stockholders' Equity [Roll Forward]
Stock options exercised (in shares)	324,995
Ending balance (in shares) at Jun. 30, 2020	26,751,091			26,751,091
Ending balance at Jun. 30, 2020	$ 233,594			$ 27		452,891		154	(219,478)
Beginning balance (in shares) at Mar. 31, 2020				24,362,389
Beginning balance at Mar. 31, 2020	127,403			$ 24		323,473		295	(196,389)
Stockholders' Equity [Roll Forward]
Stock options exercised (in shares)				70,853
Stock options exercised	732					732
Issuance of common stock (in shares)				1,119	2,300,000
Issuance of common stock	73		$ 124,654		$ 3	73	$ 124,651
Issuance of common stock for employee stock purchase plan (in shares)				16,730
Issuance of common stock for employee stock purchase plan	1,059					1,059
Stock-based compensation expense	2,903					2,903
Other comprehensive income (loss)	(141)							(141)
Net loss	$ (23,089)								(23,089)
Ending balance (in shares) at Jun. 30, 2020	26,751,091			26,751,091
Ending balance at Jun. 30, 2020	$ 233,594			$ 27		$ 452,891		$ 154	$ (219,478)