Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 3,427,741	$ 3,122,950
Other comprehensive income	4,628	12,883
Ending balance	3,565,954	3,216,781
Available-for-Sale Investment Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(28,772)	(6,144)
Net unrealized gains (losses) arising during the period	5,055	15,142
Amounts reclassified from AOCI	(1,434)	(2,226)
Other comprehensive income	3,621	12,916
Ending balance	(25,151)	6,772
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(19,374)	(8,797)
Net unrealized gains (losses) arising during the period	1,007	(33)
Amounts reclassified from AOCI	0	0
Other comprehensive income	1,007	(33)
Ending balance	(18,367)	(8,830)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(48,146)	(14,941)
Net unrealized gains (losses) arising during the period	6,062	15,109
Amounts reclassified from AOCI	(1,434)	(2,226)
Other comprehensive income	4,628	12,883
Ending balance	$ (43,518)	$ (2,058)