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 at Mar. 31, 2018	296,848	$ 0	$ 499,974	$ 0	7,284	(830)	(209,580)
Ending balance, shares at Mar. 31, 2018			78,627,369	12,394,127
Ending balance at Jun. 30, 2018		41,000
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]
Other comprehensive gain (loss), net of tax impact	(160)
Net loss	(35,483)
Ending balance at Jun. 30, 2018	276,781		$ 499,974	$ 0	8,718	(692)	(231,219)
Ending balance, shares at Jun. 30, 2018			78,627,369	12,522,598
Increase (Decrease) in Temporary Equity [Roll Forward]
Fair value adjustment of redeemable noncontrolling interest		41,000
Ending balance at Jun. 30, 2018		41,000
Beginning balance at Mar. 31, 2018	296,848	0	$ 499,974	$ 0	7,284	(830)	(209,580)
Beginning balance, shares at Mar. 31, 2018			78,627,369	12,394,127
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, shares				148,230
Issuance of common stock upon exercise of stock options	424				424
Stock-based compensation	1,180				1,180
Issuance of common stock upon exercise of warrants, shares				11,922
Issuance of common stock upon exercise of warrants	(2)				(2)
Repurchase of common stock, shares				(31,681)
Repurchase of common stock	(172)
Other comprehensive gain (loss), net of tax impact	138					138
Net loss	(21,639)						(21,639)
Ending balance at Jun. 30, 2018	276,781		$ 499,974	$ 0	8,718	(692)	(231,219)
Ending balance, shares at Jun. 30, 2018			78,627,369	12,522,598
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
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 at Mar. 31, 2019	468,134			$ 1	771,009	333	(303,209)
Ending balance, shares at Mar. 31, 2019				86,098,474.000
Beginning balance at Dec. 31, 2018		41,800
Ending balance at Jun. 30, 2019		46,800
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	1,677,990
Other comprehensive gain (loss), net of tax impact	$ 1,427
Net loss	(32,651)
Ending balance at Jun. 30, 2019	815,474			$ 1	1,128,938	1,344	(314,809)
Ending balance, shares at Jun. 30, 2019				92,806,252
Beginning balance at Mar. 31, 2019		46,500
Increase (Decrease) in Temporary Equity [Roll Forward]
Fair value adjustment of redeemable noncontrolling interest	(300)	300					(300)
Ending balance at Jun. 30, 2019		$ 46,800
Beginning balance at Mar. 31, 2019	468,134			$ 1	771,009	333	(303,209)
Beginning balance, shares at Mar. 31, 2019				86,098,474.000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon follow-on offering, shares				5,175,000
Issuance of common stock upon follow-on offering, net of offering costs of $723	349,709			$ 349,709
Issuance of common stock upon exercise of stock options, shares				1,531,672
Issuance of common stock upon exercise of stock options	$ 4,992				4,992
Vesting of restricted stock units (in shares)	1,106
Vesting of common stock exercised early	$ 13				13
Stock-based compensation	3,215				3,215
Other comprehensive gain (loss), net of tax impact	1,011					1,011
Net loss	(11,300)						(11,300)
Ending balance at Jun. 30, 2019	$ 815,474			$ 1	$ 1,128,938	$ 1,344	$ (314,809)
Ending balance, shares at Jun. 30, 2019				92,806,252