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
Issuance of common stock upon exercise of stock options and vesting of restricted stock units (in shares)	987
Issuance of common stock upon exercise of stock options and vesting of restricted stock units	$ 1	6,907	0	6,908
Tax portion of vested restricted stock units	0	(676)	0	(676)
Stock-based compensation expense (employee)	0	3,932	0	3,932
Stock-based compensation expense (non-employee)	0	75	0	75
Stock-based compensation expense (ESPP)	0	318	0	318
Net loss and comprehensive loss	$ 0	0	(4,411)	(4,411)
Issuance of common stock under employee stock purchase plan (ESPP) (in shares)	80
Issuance of common stock under employee stock purchase plan (ESPP)	$ 0	491	0	491
Sale of common stock in a public offering, net of issuance costs of $9,208 (in shares)	6,325
Sale of common stock in a public offering, net of issuance costs of $9,208	$ 6	137,842	0	137,848
Balance (in shares) at Jun. 30, 2019	48,255
Balance at Jun. 30, 2019	$ 48	462,689	(238,497)	224,240
Balance (in shares) at Mar. 31, 2019	41,509
Balance at Mar. 31, 2019	$ 42	319,733	(236,003)	83,772
Issuance of common stock upon exercise of stock options and vesting of restricted stock units (in shares)	421
Issuance of common stock upon exercise of stock options and vesting of restricted stock units	$ 0	2,668	0	2,668
Tax portion of vested restricted stock units	0	(120)	0	(120)
Stock-based compensation expense (employee)	0	2,334	0	2,334
Stock-based compensation expense (non-employee)	0	55	0	55
Stock-based compensation expense (ESPP)	0	177	0	177
Net loss and comprehensive loss	$ 0	0	(2,494)	(2,494)
Sale of common stock in a public offering, net of issuance costs of $9,208 (in shares)	6,325
Sale of common stock in a public offering, net of issuance costs of $9,208	$ 6	137,842	0	137,848
Balance (in shares) at Jun. 30, 2019	48,255
Balance at Jun. 30, 2019	$ 48	462,689	(238,497)	224,240
Balance (in shares) at Dec. 31, 2019	49,625
Balance at Dec. 31, 2019	$ 50	486,090	(246,685)	239,455
Issuance of common stock upon exercise of stock options and vesting of restricted stock units (in shares)	760
Issuance of common stock upon exercise of stock options and vesting of restricted stock units	$ 0	4,745	0	4,745
Tax portion of vested restricted stock units	0	(2,678)	0	(2,678)
Stock-based compensation expense (employee)	0	5,560	0	5,560
Stock-based compensation expense (non-employee)	0	20	0	20
Stock-based compensation expense (ESPP)	0	685	0	685
Net loss and comprehensive loss	$ 0	0	(22,741)	(22,741)
Issuance of common stock under employee stock purchase plan (ESPP) (in shares)	61
Issuance of common stock under employee stock purchase plan (ESPP)	$ 0	1,101	0	1,101
Balance (in shares) at Jun. 30, 2020	50,446
Balance at Jun. 30, 2020	$ 50	495,523	(269,426)	226,147
Balance (in shares) at Mar. 31, 2020	50,000
Balance at Mar. 31, 2020	$ 50	488,773	(258,401)	230,422
Issuance of common stock upon exercise of stock options and vesting of restricted stock units (in shares)	446
Issuance of common stock upon exercise of stock options and vesting of restricted stock units	$ 0	3,764	0	3,764
Tax portion of vested restricted stock units	0	(374)	0	(374)
Stock-based compensation expense (employee)	0	3,009	0	3,009
Stock-based compensation expense (non-employee)	0	20	0	20
Stock-based compensation expense (ESPP)	0	331	0	331
Net loss and comprehensive loss	$ 0	0	(11,025)	(11,025)
Balance (in shares) at Jun. 30, 2020	50,446
Balance at Jun. 30, 2020	$ 50	$ 495,523	$ (269,426)	$ 226,147