Condensed Consolidated Statements of Shareholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Ordinary Shares [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2018	$ 1,190,106	$ 17	$ (4,585)	$ 2,374,966	$ (1,523)	$ (1,178,769)
Beginning balance, shares at Dec. 31, 2018		169,244,520	384,366
Cumulative effect adjustments from adoption of ASU 2016-02	64					64
Issuance of ordinary shares - public offering	326,849	$ 1		326,848
Issuance of ordinary shares - public offering, shares		14,081,632
Issuance of ordinary shares in conjunction with vesting of restricted stock units and stock option exercises	10,042			10,042
Issuance of ordinary shares in conjunction with vesting of restricted stock units and stock option exercises, shares		1,804,196
Ordinary shares withheld for payment of employees’ withholding tax liability	(17,171)			(17,171)
Share-based compensation	27,548			27,548
Currency translation adjustment	(487)				(487)
Net loss	(32,863)					(32,863)
Ending balance at Mar. 31, 2019	1,504,088	$ 18	$ (4,585)	2,722,233	(2,010)	(1,211,568)
Ending balance, shares at Mar. 31, 2019		185,130,348	384,366
Beginning balance at Dec. 31, 2018	1,190,106	$ 17	$ (4,585)	2,374,966	(1,523)	(1,178,769)
Beginning balance, shares at Dec. 31, 2018		169,244,520	384,366
Currency translation adjustment	(143)
Net loss	(37,983)
Ending balance at Jun. 30, 2019	1,520,873	$ 19	$ (4,585)	2,743,793	(1,666)	(1,216,688)
Ending balance, shares at Jun. 30, 2019		186,470,230	384,366
Beginning balance at Mar. 31, 2019	1,504,088	$ 18	$ (4,585)	2,722,233	(2,010)	(1,211,568)
Beginning balance, shares at Mar. 31, 2019		185,130,348	384,366
Issuance of ordinary shares - public offering	(55)			(55)
Issuance of ordinary shares in conjunction with vesting of restricted stock units and stock option exercises	1,987	$ 1		1,986
Issuance of ordinary shares in conjunction with vesting of restricted stock units and stock option exercises, shares		781,026
Issuance of ordinary shares in conjunction with ESPP program	5,465			5,465
Issuance of ordinary shares in conjunction with ESPP programs, shares		558,856
Ordinary shares withheld for payment of employees’ withholding tax liability	(7,203)			(7,203)
Share-based compensation	21,367			21,367
Currency translation adjustment	344				344
Net loss	(5,120)					(5,120)
Ending balance at Jun. 30, 2019	1,520,873	$ 19	$ (4,585)	2,743,793	(1,666)	(1,216,688)
Ending balance, shares at Jun. 30, 2019		186,470,230	384,366
Beginning balance at Dec. 31, 2019	2,185,449	$ 19	$ (4,585)	2,797,602	(1,905)	(605,682)
Beginning balance, shares at Dec. 31, 2019		188,402,040	384,366
Issuance of ordinary shares in conjunction with the exercise of stock options and the vesting of restricted stock and performance stock units	7,049			7,049
Issuance of ordinary shares in conjunction with warrant exercises, shares		2,560,573
Ordinary shares withheld for payment of employees’ withholding tax liability	(46,664)			(46,664)
Share-based compensation	56,421			56,421
Currency translation adjustment	(325)				(325)
Net loss	(13,591)					(13,591)
Ending balance at Mar. 31, 2020	2,188,339	$ 19	$ (4,585)	2,814,408	(2,230)	(619,273)
Ending balance, shares at Mar. 31, 2020		190,962,613	384,366
Beginning balance at Dec. 31, 2019	2,185,449	$ 19	$ (4,585)	2,797,602	(1,905)	(605,682)
Beginning balance, shares at Dec. 31, 2019		188,402,040	384,366
Currency translation adjustment	19
Net loss	(93,601)
Ending balance at Jun. 30, 2020	2,361,852	$ 20	$ (4,585)	3,067,586	(1,886)	(699,283)
Ending balance, shares at Jun. 30, 2020		199,991,807	384,366
Beginning balance at Mar. 31, 2020	2,188,339	$ 19	$ (4,585)	2,814,408	(2,230)	(619,273)
Beginning balance, shares at Mar. 31, 2020		190,962,613	384,366
Issuance of ordinary shares in conjunction with the exercise of stock options and the vesting of restricted stock and performance stock units	18,838			18,838
Issuance of ordinary shares in conjunction with warrant exercises, shares		1,427,108
Issuance of ordinary shares in conjunction with ESPP program	7,979			7,979
Issuance of ordinary shares in conjunction with ESPP programs, shares		376,718
Issuance of ordinary shares in conjunction with Exchangeable Senior Notes	205,650	$ 1		205,649
Issuance of ordinary shares in conjunction with Exchangeable Senior Notes, shares		7,225,368
Ordinary shares withheld for payment of employees’ withholding tax liability	(6,345)			(6,345)
Share-based compensation	27,057			27,057
Currency translation adjustment	344				344
Net loss	(80,010)					(80,010)
Ending balance at Jun. 30, 2020	$ 2,361,852	$ 20	$ (4,585)	$ 3,067,586	$ (1,886)	$ (699,283)
Ending balance, shares at Jun. 30, 2020		199,991,807	384,366