Summary of Significant Accounting Policies - Summarized Financial Information for the Equity Method Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Operating expenses	$ 82,038	$ 92,317
Operating loss	(58,703)	(52,651)
Other, net	(2,371)	3,616
Equity Method Investments
Schedule of Equity Method Investments [Line Items]
Current assets	10,753		$ 17,485
Noncurrent assets	32,935		31,274
Total assets	43,688		48,759
Current liabilities	3,766		4,226
Net assets	39,922		$ 44,533
Revenues	98	67
Operating expenses	5,377	8,610
Operating loss	(5,279)	(8,543)
Other, net	4	14
Net loss	$ (5,275)	$ (8,529)