Summary of Significant Accounting Policies - Adoption of Topic 606 and ASC 842, Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss	$ (49,515)	$ (47,524)	$ (71,727)	$ (91,420)	$ (56,035)	$ (82,815)	$ (73,610)	$ (75,155)	$ (260,186)	$ (287,615)	$ (320,839)
Net cash used in operating activities										(96,103)	(200,141)
Net cash used in investing activities										(777,319)	(695,802)
Net cash provided by financing activities										890,849	899,145
Net change in cash and restricted cash(1)										17,427	3,202
Cash and restricted cash, beginning of period				241,790				224,363	241,790	224,363	221,161
Cash and restricted cash, end of period	$ 304,399				241,790				304,399	241,790	224,363
Previously Reported
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss										(286,734)	(303,301)
Net cash used in operating activities										(61,011)	(150,580)
Net cash used in investing activities										(812,327)	(745,112)
Net cash provided by financing activities										869,499	898,192
Net change in cash and restricted cash(1)										(3,839)	2,500
Cash and restricted cash, beginning of period				202,525				206,364	202,525	206,364	203,864
Cash and restricted cash, end of period					202,525					202,525	206,364
Adoption Impact | Accounting Standards Update 2014-09, Topic 230 and ASC 842
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net loss										(881)	(17,538)
Net cash used in operating activities										(35,092)	(49,561)
Net cash used in investing activities										35,008	49,310
Net cash provided by financing activities										21,350	953
Net change in cash and restricted cash(1)										21,266	702
Cash and restricted cash, beginning of period				$ 39,265				$ 17,999	$ 39,265	17,999	17,297
Cash and restricted cash, end of period					$ 39,265					$ 39,265	$ 17,999