CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit	Total
Balance at beginning of period at Dec. 31, 2018		$ 507,366	$ (69)	$ (292,173)	$ 215,124
Balance at beginning of period (in shares) at Dec. 31, 2018	41,210,725
Increase (Decrease) in Stockholders' Equity
Vesting of RSUs		(188)			(188)
Vesting of RSUs, shares	58,918
Unrealized gain on marketable securities			34		34
Foreign currency translation adjustment			(14)		(14)
Stock-based compensation expense		4,862			4,862
Net loss				(37,565)	(37,565)
Balance at end of period at Mar. 31, 2019		512,040	(49)	(329,738)	182,253
Balance at end of period (in shares) at Mar. 31, 2019	41,269,643
Balance at beginning of period at Dec. 31, 2019		523,505	(66)	(453,527)	$ 69,912
Balance at beginning of period (in shares) at Dec. 31, 2019	41,485,638				41,485,638
Increase (Decrease) in Stockholders' Equity
Vesting of RSUs		(95)			$ (95)
Vesting of RSUs, shares	346,582
Fair value of warrants issued		378			378
Unrealized gain on marketable securities			60		60
Foreign currency translation adjustment			53		53
Stock-based compensation expense		3,453			3,453
Net loss				(15,586)	(15,586)
Balance at end of period at Mar. 31, 2020		$ 527,241	$ 47	$ (469,113)	$ 58,175
Balance at end of period (in shares) at Mar. 31, 2020	41,832,220				41,832,220