Consolidated Statements of Redeemable Noncontrolling Interest and Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Redeemable Noncontrolling Interest	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance at Dec. 31, 2017	$ 308,606		$ 499,974	$ 0	$ 4,900	$ (532)	$ (195,736)
Beginning balance, shares at Dec. 31, 2017			78,627,369	11,896,882
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, shares				421,264
Issuance of common stock upon exercise of stock options	1,103				1,103
Stock-based compensation	1,277				1,277
Issuance of common stock upon early exercise of stock options, shares				44,268
Issuance of common stock upon exercise of warrants, shares				31,713
Issuance of common stock upon exercise of warrants	(4)				(4)
Other comprehensive gain (loss), net of tax impact	(298)					(298)
Net loss	(13,844)						(13,844)
Ending balance, shares at Mar. 31, 2018			78,627,369	12,394,127
Ending balance at Mar. 31, 2018	296,848		$ 499,974	$ 0	7,284	(830)	(209,580)
Beginning balance at Dec. 31, 2018		$ 41,800
Increase (Decrease) in Temporary Equity [Roll Forward]
Fair value adjustment of redeemable noncontrolling interest	(4,700)	4,700					(4,700)
Ending balance at Mar. 31, 2019		$ 46,500
Beginning balance at Dec. 31, 2018	$ 483,152			$ 1	764,033	(83)	(280,799)
Beginning balance, shares at Dec. 31, 2018				85,832,454
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, shares	146,318			146,318
Issuance of common stock upon exercise of stock options	$ 538				538
Vesting of common stock exercised early	56				56
Stock-based compensation	3,183				3,183
Common stock issued under employee stock purchase plan (in shares)				119,702
Common stock issued under employee stock purchase plan	1,933				1,933
Other comprehensive gain (loss), net of tax impact	416					416
Net loss	(21,351)						(21,351)
Ending balance, shares at Mar. 31, 2019				86,098,474
Ending balance at Mar. 31, 2019	$ 468,134			$ 1	$ 771,009	$ 333	$ (303,209)