Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Total
Balance (in shares) at Dec. 31, 2018	40,863
Balance at Dec. 31, 2018	$ 41	$ 313,800	$ (234,086)	$ 79,755
Sale of common stock in a public offering, net of offering costs (in shares)	6,325
Sale of common stock in a public offering, net of offering costs	$ 6	137,842	0	137,848
Issuance of common stock upon exercise of stock options and vesting of restricted stock units (in shares)	1,498
Issuance of common stock upon exercise of stock options and vesting of restricted stock units	$ 2	11,139	0	11,141
Issuance of common stock under ESPP (in shares)	136
Issuance of common stock under ESPP	$ 0	1,266	0	1,266
Tax portion of vested restricted stock units	0	(810)	0	(810)
Stock-based compensation expense (employee)	0	6,255	0	6,255
Stock-based compensation expense (non-employee)	0	138	0	138
Stock-based compensation expense (ESPP)	0	572	0	572
Net loss and comprehensive loss	$ 0	0	(5,141)	(5,141)
Balance (in shares) at Sep. 30, 2019	48,822
Balance at Sep. 30, 2019	$ 49	470,202	(239,227)	231,024
Balance (in shares) at Jun. 30, 2019	48,255
Balance at Jun. 30, 2019	$ 48	462,689	(238,497)	224,240
Issuance of common stock upon exercise of stock options and vesting of restricted stock units (in shares)	511
Issuance of common stock upon exercise of stock options and vesting of restricted stock units	$ 1	4,231	0	4,232
Issuance of common stock under ESPP (in shares)	56
Issuance of common stock under ESPP	$ 0	774	0	774
Tax portion of vested restricted stock units	0	(132)	0	(132)
Stock-based compensation expense (employee)	0	2,324	0	2,324
Stock-based compensation expense (non-employee)	0	62	0	62
Stock-based compensation expense (ESPP)	0	254	0	254
Net loss and comprehensive loss	$ 0	0	(730)	(730)
Balance (in shares) at Sep. 30, 2019	48,822
Balance at Sep. 30, 2019	$ 49	470,202	(239,227)	231,024
Balance (in shares) at Dec. 31, 2019	49,625
Balance at Dec. 31, 2019	$ 50	486,090	(246,685)	239,455
Sale of common stock in a public offering, net of offering costs (in shares)	6,900
Sale of common stock in a public offering, net of offering costs	$ 7	193,824	0	193,831
Issuance of common stock upon exercise of stock options and vesting of restricted stock units (in shares)	1,187
Issuance of common stock upon exercise of stock options and vesting of restricted stock units	$ 1	8,073	0	8,074
Issuance of common stock under ESPP (in shares)	102
Issuance of common stock under ESPP	$ 0	2,037	0	2,037
Tax portion of vested restricted stock units	0	(3,161)	0	(3,161)
Stock-based compensation expense (employee)	0	8,591	0	8,591
Stock-based compensation expense (non-employee)	0	35	0	35
Stock-based compensation expense (ESPP)	0	728	0	728
Net loss and comprehensive loss	$ 0	0	(26,865)	(26,865)
Balance (in shares) at Sep. 30, 2020	57,814
Balance at Sep. 30, 2020	$ 58	696,217	(273,550)	422,725
Balance (in shares) at Jun. 30, 2020	50,446
Balance at Jun. 30, 2020	$ 50	495,523	(269,426)	226,147
Sale of common stock in a public offering, net of offering costs (in shares)	6,900
Sale of common stock in a public offering, net of offering costs	$ 7	193,824	0	193,831
Issuance of common stock upon exercise of stock options and vesting of restricted stock units (in shares)	427
Issuance of common stock upon exercise of stock options and vesting of restricted stock units	$ 1	3,328	0	3,329
Issuance of common stock under ESPP (in shares)	41
Issuance of common stock under ESPP	$ 0	935	0	935
Tax portion of vested restricted stock units	0	(483)	0	(483)
Stock-based compensation expense (employee)	0	3,032	0	3,032
Stock-based compensation expense (non-employee)	0	15	0	15
Stock-based compensation expense (ESPP)	0	43	0	43
Net loss and comprehensive loss	$ 0	0	(4,124)	(4,124)
Balance (in shares) at Sep. 30, 2020	57,814
Balance at Sep. 30, 2020	$ 58	$ 696,217	$ (273,550)	$ 422,725