CONDENSED CONSOLIDATED STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' DEFICIT - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance, shares (in shares) at Dec. 31, 2017	308,373,000
Beginning balance at Dec. 31, 2017	$ 1,465,399
Ending balance, shares (in shares) at Mar. 31, 2018	308,373,000
Ending balance at Mar. 31, 2018	$ 1,465,399
Beginning balance (in shares) at Dec. 31, 2017		126,771,000
Beginning balance at Dec. 31, 2017	(546,464)	$ 1	$ 236,682	$ (766)	$ (782,381)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for cash upon exercise of stock options, net (in shares)		140,000
Issuance of common stock for cash upon exercise of stock options, net	435		435
Share-based compensation expense	4,834		4,834
Other comprehensive loss	(1,059)			(1,059)
Net loss attributable to common stockholders	(52,709)				(52,709)
Ending balance (in shares) at Mar. 31, 2018		126,911,000
Ending balance at Mar. 31, 2018	$ (594,963)	$ 1	241,951	(1,825)	(835,090)
Beginning balance, shares (in shares) at Dec. 31, 2018	308,373,000
Beginning balance at Dec. 31, 2018	$ 1,465,399
Ending balance, shares (in shares) at Mar. 31, 2019	308,373,000
Ending balance at Mar. 31, 2019	$ 1,465,399
Beginning balance (in shares) at Dec. 31, 2018		127,298,000
Beginning balance at Dec. 31, 2018	$ (594,563)	$ 1	252,212	(1,421)	(845,355)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for cash upon exercise of stock options, net (in shares)	73,000	73,000
Issuance of common stock for cash upon exercise of stock options, net	$ 110		110
Share-based compensation expense	694		694
Other comprehensive loss	1,190			1,190
Net loss attributable to common stockholders	(41,420)				(41,420)
Ending balance (in shares) at Mar. 31, 2019		127,371,000
Ending balance at Mar. 31, 2019	$ (633,989)	$ 1	$ 253,016	$ (231)	$ (886,775)