Condensed Consolidated Statements of Redeemable Noncontrolling Interest and Stockholders’ Equity (unaudited) - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Redeemable Noncontrolling Interest	Common Stock	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Beginning balance at Dec. 31, 2018			$ 41,800
Increase (Decrease) in Temporary Equity [Roll Forward]
Adjustment of redeemable noncontrolling interest	$ (5,000)		5,000					$ (5,000)
Ending balance at Jun. 30, 2019			46,800
Beginning balance (in shares) at Dec. 31, 2018				85,832,454
Beginning balance at Dec. 31, 2018	483,152			$ 1	$ 764,033		$ (83)	(280,799)
Beginning balance (Topic 606 adoption) at Dec. 31, 2018		$ 4,907							$ 4,907
Beginning balance (ASU 2018-07 adoption) at Dec. 31, 2018						$ 1,266			$ (1,266)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net of offering costs (in shares)				5,175,000
Issuance of common stock in public offering, net of offering costs	349,709				349,709
Issuance of common stock upon exercise of stock options (in shares)				1,677,990
Issuance of common stock upon exercise of stock options	5,530				5,530
Vesting of restricted stock units (in shares)				1,106
Vesting of common stock exercised early	69				69
Common stock issued under employee stock purchase plan (in shares)				119,702
Common stock issued under employee stock purchase plan	1,933				1,933
Stock-based compensation	6,398				6,398
Other comprehensive loss	1,427						1,427
Net loss	(32,651)							(32,651)
Ending balance (in shares) at Jun. 30, 2019				92,806,252
Ending balance at Jun. 30, 2019	815,474			$ 1	1,128,938		1,344	(314,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to additional paid in capital, stock issued, issuance costs	723
Beginning balance at Mar. 31, 2019			46,500
Increase (Decrease) in Temporary Equity [Roll Forward]
Adjustment of redeemable noncontrolling interest	(300)		300					(300)
Ending balance at Jun. 30, 2019			46,800
Beginning balance (in shares) at Mar. 31, 2019				86,098,474
Beginning balance at Mar. 31, 2019	468,134			$ 1	771,009		333	(303,209)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net of offering costs (in shares)				5,175,000
Issuance of common stock in public offering, net of offering costs	349,709				349,709
Issuance of common stock upon exercise of stock options (in 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 loss	1,011						1,011
Net loss	(11,300)							(11,300)
Ending balance (in shares) at Jun. 30, 2019				92,806,252
Ending balance at Jun. 30, 2019	815,474			$ 1	1,128,938		1,344	(314,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to additional paid in capital, stock issued, issuance costs	723
Beginning balance at Dec. 31, 2019			49,600
Increase (Decrease) in Temporary Equity [Roll Forward]
Adjustment of redeemable noncontrolling interest	(800)		800					(800)
Ending balance at Jun. 30, 2020			50,400
Beginning balance (in shares) at Dec. 31, 2019				94,261,414
Beginning balance at Dec. 31, 2019	798,393			$ 1	1,150,090		1,111	(352,809)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net of offering costs (in shares)				4,312,500
Issuance of common stock in public offering, net of offering costs	$ 354,600				354,600
Issuance of common stock upon exercise of stock options (in shares)	654,557			654,557
Issuance of common stock upon exercise of stock options	$ 3,548				3,548
Vesting of restricted stock units (in shares)				25,602
Vesting of common stock exercised early	26				26
Common stock issued under employee stock purchase plan (in shares)				58,164
Common stock issued under employee stock purchase plan	3,956				3,956
Stock-based compensation	32,153				32,153
Other comprehensive loss	4,281						4,281
Net loss	(81,568)							(81,568)
Ending balance (in shares) at Jun. 30, 2020				99,312,237
Ending balance at Jun. 30, 2020	1,114,589			$ 1	1,544,373		5,392	(435,177)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to additional paid in capital, stock issued, issuance costs	1,130
Beginning balance at Mar. 31, 2020			45,500
Increase (Decrease) in Temporary Equity [Roll Forward]
Adjustment of redeemable noncontrolling interest	(4,900)		4,900					(4,900)
Ending balance at Jun. 30, 2020			$ 50,400
Beginning balance (in shares) at Mar. 31, 2020				94,509,011
Beginning balance at Mar. 31, 2020	785,113			$ 1	1,157,945		7,705	(380,538)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in public offering, net of offering costs (in shares)				4,312,500
Issuance of common stock in public offering, net of offering costs	354,600				354,600
Issuance of common stock upon exercise of stock options (in shares)				412,554
Issuance of common stock upon exercise of stock options	2,044				2,044
Vesting of restricted stock units (in shares)				20,008
Vesting of common stock exercised early	13				13
Common stock issued under employee stock purchase plan (in shares)				58,164
Common stock issued under employee stock purchase plan	3,956				3,956
Stock-based compensation	25,815				25,815
Other comprehensive loss	(2,313)						(2,313)
Net loss	(49,739)							(49,739)
Ending balance (in shares) at Jun. 30, 2020				99,312,237
Ending balance at Jun. 30, 2020	1,114,589			$ 1	$ 1,544,373		$ 5,392	$ (435,177)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustments to additional paid in capital, stock issued, issuance costs	$ 1,130