Income Taxes (Loss from Operations before Income Tax Expense by Jurisdiction) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net loss	$ (50,843)	$ (44,607)	$ (44,465)	$ (43,854)	$ (57,109)	$ (66,254)	$ (79,351)	$ (77,252)	$ (183,769)	$ (279,966)	$ (156,937)
Domestic Tax Authority [Member]
Net loss									(173,749)	(273,134)	(150,227)
Foreign Tax Authority [Member]
Net loss									$ (10,020)	$ (6,832)	$ (6,710)