Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common stock	Treasury stock	Additional paid-in capital	Accumulated deficit
Balance, beginning of year at Dec. 31, 2016	$ 83,617	$ 186	$ (260)	$ 299,133	$ (215,442)
Balance, beginning of year (in shares) at Dec. 31, 2016		18,671,409	72,727
Employee stock-based compensation expense	6,766			6,766
Stock option exercises	1,346	$ 5		1,341
Stock option exercises (in shares)		480,236
Employee stock purchase program (ESPP)	647	$ 1		646
Employee stock purchase program (ESPP) (in shares)		108,081
Vested restricted stock		$ 3		(3)
Vested restricted stock (in shares)		293,910
Shares withheld for tax obligations on vested RSUs	(725)	$ (1)		(724)
Shares withheld for tax obligations on vested RSUs, shares		(78,934)
Net loss	(64,028)				(64,028)
Balance, end of year at Dec. 31, 2017	27,623	$ 194	$ (260)	307,159	(279,470)
Balance, end of year (in shares) at Dec. 31, 2017		19,474,702	72,727
Proceeds from follow-on offering, net of costs	107,551	$ 85		107,466
Proceeds from follow-on offering, net of costs (in shares)		8,518,519
Employee stock-based compensation expense	13,824			13,824
Stock option exercises	1,149	$ 1		1,148
Stock option exercises (in shares)		147,463
Employee stock purchase program (ESPP)	993	$ 2		991
Employee stock purchase program (ESPP) (in shares)		145,616
Vested restricted stock		$ 5		(5)
Vested restricted stock (in shares)		523,257
Shares withheld for tax obligations on vested RSUs	(1,635)	$ (1)		(1,634)
Shares withheld for tax obligations on vested RSUs, shares		(108,063)
Net loss	(82,627)				(82,627)
Balance, end of year at Dec. 31, 2018	66,878	$ 286	$ (260)	428,949	(362,097)
Balance, end of year (in shares) at Dec. 31, 2018		28,701,494	72,727
Proceeds from follow-on offering, net of costs	107,734	$ 200		107,534
Proceeds from follow-on offering, net of costs (in shares)		20,000,000
Employee stock-based compensation expense	12,655			12,655
Stock option exercises	125			125
Stock option exercises (in shares)		51,451
Employee stock purchase program (ESPP)	1,216	$ 1		1,215
Employee stock purchase program (ESPP) (in shares)		175,624
Vested restricted stock		$ 10		(10)
Vested restricted stock (in shares)		944,467
Shares withheld for tax obligations on vested RSUs	(3,064)	$ (2)		(3,062)
Shares withheld for tax obligations on vested RSUs, shares		(260,129)
Equity contingent consideration	3,156			3,156
Net loss	(106,818)				(106,818)
Balance, end of year at Dec. 31, 2019	$ 81,882	$ 495	$ (260)	$ 550,562	$ (468,915)
Balance, end of year (in shares) at Dec. 31, 2019		49,612,907	72,727