Unaudited Condensed Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Revision of Prior Period Accounting Standards Update Adjustment [Member]	Common Stock	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Revision of Prior Period Accounting Standards Update Adjustment [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Revision of Prior Period Accounting Standards Update Adjustment [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2019	$ (398,890)		$ 9	$ 979,499		$ (2,256)	$ (1,376,142)
Beginning Balance, Shares at Dec. 31, 2019			88,240,877
Net loss	(170,757)						(170,757)
Currency translation adjustments	(2,602)					(2,602)
Stock-based compensation expense	7,159			7,159
Issuance of common stock upon vesting of restricted stock units and restricted stock awards, Shares			641,428
Tax withholding related to vesting of restricted stock units	(809)			(809)
Issuance of common stock in connection with employee stock purchase plan	547			547
Issuance of common stock in connection with employee stock purchase plan, Shares			227,438
Settlement of prepaid forward shares [value]			$ (1)	98,858					$ (98,857)
Settlement of prepaid forward shares [shares]			(5,077,400)						5,077,400
Ending Balance at Jun. 30, 2020	(569,017)	$ (3,665)	$ 8	1,085,254		(4,858)	(1,550,564)	$ (3,665)	$ (98,857)
Ending Balance, Shares at Jun. 30, 2020			84,032,343						5,077,400
Beginning Balance at Mar. 31, 2020	(486,606)		$ 8	1,081,955		(5,127)	(1,464,585)		$ (98,857)
Beginning Balance, Shares at Mar. 31, 2020			83,773,648						5,077,400
Net loss	(85,979)						(85,979)
Currency translation adjustments	269					269
Stock-based compensation expense	3,164			3,164
Issuance of common stock upon vesting of restricted stock units and restricted stock awards, Shares			118,938
Tax withholding related to vesting of restricted stock units	(127)			(127)
Issuance of common stock in connection with employee stock purchase plan	262			262
Issuance of common stock in connection with employee stock purchase plan, Shares			139,757
Ending Balance at Jun. 30, 2020	(569,017)	(3,665)	$ 8	1,085,254		(4,858)	(1,550,564)	(3,665)	$ (98,857)
Ending Balance, Shares at Jun. 30, 2020			84,032,343						5,077,400
Beginning Balance at Dec. 31, 2020	(641,114)		$ 9	1,088,590		(1,013)	(1,629,843)		$ (98,857)
Beginning Balance, Shares at Dec. 31, 2020			85,990,499						5,077,400
Net loss	(76,933)						(76,933)
Currency translation adjustments	138					138
Fair value adjustments of cash flow hedge, net of tax	(430)					(430)
Stock-based compensation expense	11,312			11,312
Issuance of common stock upon exercise of stock options	$ 544			544
Issuance of common stock upon exercise of stock options, shares	212,397		212,397
Issuance of common stock upon vesting of restricted stock units and restricted stock awards, Shares			654,072
Tax withholding related to vesting of restricted stock units	$ (3,544)			(3,544)
Issuance of common stock in connection with employee stock purchase plan	247			247
Issuance of common stock in connection with employee stock purchase plan, Shares			23,669
Settlement of convertible notes	154,441		$ 2	154,439
Settlement of convertible notes shares			24,353,006
Settlement of prepaid forward shares [value]				29,946					$ (29,946)
Settlement of prepaid forward shares [shares]			(1,538,049)						1,538,049
Ending Balance at Jun. 30, 2021	(577,282)	(21,943)	$ 11	1,234,111	$ (47,423)	(1,305)	(1,681,296)	25,480	$ (128,803)
Ending Balance, Shares at Jun. 30, 2021			109,695,594						6,615,449
Beginning Balance at Mar. 31, 2021	(631,503)		$ 9	1,080,305		(912)	(1,612,048)		$ (98,857)
Beginning Balance, Shares at Mar. 31, 2021			92,071,085						5,077,400
Net loss	(69,248)						(69,248)
Currency translation adjustments	37					37
Fair value adjustments of cash flow hedge, net of tax	(430)					(430)
Stock-based compensation expense	3,385			3,385
Issuance of common stock upon exercise of stock options	86			86
Issuance of common stock upon exercise of stock options, shares			34,751
Issuance of common stock upon vesting of restricted stock units and restricted stock awards, Shares			51,246
Tax withholding related to vesting of restricted stock units	(324)			(324)
Issuance of common stock in connection with employee stock purchase plan	131			131
Issuance of common stock in connection with employee stock purchase plan, Shares			12,032
Settlement of convertible notes	120,584		$ 2	120,582
Settlement of convertible notes shares			19,064,529
Settlement of prepaid forward shares [value]				29,946					$ (29,946)
Settlement of prepaid forward shares [shares]			(1,538,049)						1,538,049
Ending Balance at Jun. 30, 2021	$ (577,282)	$ (21,943)	$ 11	$ 1,234,111	$ (47,423)	$ (1,305)	$ (1,681,296)	$ 25,480	$ (128,803)
Ending Balance, Shares at Jun. 30, 2021			109,695,594						6,615,449