Summary of Significant Accounting Policies - Summarized Unaudited Financial Information for the Equity Method Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Operating expenses	$ 92,317	$ 85,128
Operating loss	(52,651)	(31,381)
Other, net	3,616	3,418
Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Current assets	57,724		$ 61,086
Non-current assets	15,553		13,598
Total assets	73,277		74,684
Current liabilities	7,946		6,213
Net assets	65,331		$ 68,471
Revenues	67	30
Operating expenses	8,610	13,343
Operating loss	(8,543)	(13,313)
Other, net	14	5
Net loss	$ (8,529)	$ (13,308)