Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in other comprehensive loss, net of tax	$ 2,188,053	$ 2,701,589	$ 5,924,146	$ 5,967,976
Net unrealized gains
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in other comprehensive loss, net of tax	549	895
Foreign currency translation loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in other comprehensive loss, net of tax	(339,195)	(354,329)
Accumulated other comprehensive loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Change in other comprehensive loss, net of tax	$ (338,646)	$ (353,434)