Income Taxes - Components of Loss Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Loss before income taxes	$ (129,700)	$ (194,151)	$ (86,978)
Domestic
Income Tax [Line Items]
Loss before income taxes	(71,343)	(157,067)	(69,287)
Foreign
Income Tax [Line Items]
Loss before income taxes	$ (58,357)	$ (37,084)	$ (17,691)