Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance, (shares) at Dec. 31, 2018		110,525,141
Beginning Balance at Dec. 31, 2018	$ 271,410	$ 110	$ 886,740	$ (3,702)	$ (611,738)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(19,259)				(19,259)
Other comprehensive loss, net	(390)			(390)
Recognition of stock-based compensation expense	7,481		7,481
Issuance of common stock to 401(k) plan for employees (shares)		47,347
Issuance of common stock to 401(k) plan for employees	519		519
Issuance of common stock upon exercise of stock options (shares)		146,785
Issuance of common stock upon exercise of stock options	831			831
Restricted stock award grants, net of forfeitures (shares)		259,539
Restricted stock award grants, net of forfeitures	1	$ 1
Issuance of common stock upon vesting of restricted stock units (shares)		233,760
Issuance of common stock upon vesting of restricted stock units	0
Ending Balance, (shares) at Mar. 31, 2019		111,212,572
Ending Balance at Mar. 31, 2019	260,593	$ 111	895,571	(4,092)	(630,997)
Beginning Balance, (shares) at Dec. 31, 2019		113,299,612
Beginning Balance at Dec. 31, 2019	190,393	$ 113	918,205	(3,498)	(724,427)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(40,572)				(40,572)
Other comprehensive loss, net	(1,329)			(1,329)
Recognition of stock-based compensation expense	5,010		5,010
Issuance of common stock to 401(k) plan for employees (shares)		96,959
Issuance of common stock to 401(k) plan for employees	265		265
Restricted stock award grants, net of forfeitures (shares)		1,377,508
Restricted stock award grants, net of forfeitures	1	$ 1
Ending Balance, (shares) at Mar. 31, 2020		114,774,079
Ending Balance at Mar. 31, 2020	$ 153,768	$ 114	$ 923,480	$ (4,827)	$ (764,999)