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)
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)
Stockholders' Equity [Roll Forward]
Stock options exercised (in shares)				136,791
Stock options exercised	191					191
Issuance of common stock (in shares)				848
Issuance of common stock	58					58
Stock-based compensation expense	1,524					1,524
Other comprehensive income (loss)	39							39
Net loss	(8,247)								(8,247)
Ending balance (in shares) at Sep. 30, 2019				24,038,369
Ending balance at Sep. 30, 2019	$ 146,054			$ 24		317,016		90	(171,076)
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)
Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
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)	493,965
Ending balance (in shares) at Sep. 30, 2020	26,920,845			26,920,845
Ending balance at Sep. 30, 2020	$ 228,823			$ 27		458,586		73	(229,863)
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
Ending balance at Jun. 30, 2020	233,594			$ 27		452,891		154	(219,478)
Stockholders' Equity [Roll Forward]
Stock options exercised (in shares)				168,970
Stock options exercised	2,312					2,312
Issuance of common stock (in shares)				784
Issuance of common stock	72					72
Stock-based compensation expense	3,311					3,311
Other comprehensive income (loss)	(81)							(81)
Net loss	$ (10,385)								(10,385)
Ending balance (in shares) at Sep. 30, 2020	26,920,845			26,920,845
Ending balance at Sep. 30, 2020	$ 228,823			$ 27		$ 458,586		$ 73	$ (229,863)