Summary of Significant Accounting Policies - Summarized Unaudited Financial Information for the Equity Method Investments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Operating expenses	$ 90,763	$ 77,806	$ 265,351	$ 237,500
Operating loss	(44,747)	(28,821)	(111,398)	(92,576)
Other	6,086	4,647	27,632	(39,125)
Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Current assets	68,021		68,021		$ 77,761
Non-current assets	12,856		12,856		11,040
Total assets	80,877		80,877		88,801
Current liabilities	9,032		9,032		11,588
Non-current liabilities	2,400		2,400		0
Total liabilities	11,432		11,432		11,588
Net assets	69,445		69,445		$ 77,213
Revenues	58	65	175	394
Operating expenses	9,693	18,363	33,128	50,406
Operating loss	(9,635)	(18,298)	(32,953)	(50,012)
Other	(145)	75	37	1,502
Net loss	$ (9,780)	$ (18,223)	$ (32,916)	$ (48,510)