Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 4,902,985	$ 4,591,930	$ 5,017,617	$ 4,423,974
Other comprehensive income	16,253	23,011	41,542	48,202
Ending balance	4,987,243	4,734,593	4,987,243	4,734,593
AFS Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	25,034	(23,810)	(2,419)	(45,821)
Net unrealized gains (losses) arising during the period	24,606	30,046	53,136	53,157
Amounts reclassified from AOCI	(6,790)	(1,019)	(7,867)	(2,119)
Other comprehensive income	17,816	29,027	45,269	51,038
Ending balance	42,850	5,217	42,850	5,217
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	0	0	0	0
Net unrealized gains (losses) arising during the period	(1,063)	0	(1,063)	0
Amounts reclassified from AOCI	(270)	0	(270)	0
Other comprehensive income	(1,333)	0	(1,333)	0
Ending balance	(1,333)	0	(1,333)	0
Foreign Currency Translation Adjustments, Net of Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(18,153)	(9,173)	(15,989)	(12,353)
Net unrealized gains (losses) arising during the period	(230)	(6,016)	(2,394)	(2,836)
Amounts reclassified from AOCI	0	0	0	0
Other comprehensive income	(230)	(6,016)	(2,394)	(2,836)
Ending balance	(18,383)	(15,189)	(18,383)	(15,189)
AOCI, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	6,881	(32,983)	(18,408)	(58,174)
Net unrealized gains (losses) arising during the period	23,313	24,030	49,679	50,321
Amounts reclassified from AOCI	(7,060)	(1,019)	(8,137)	(2,119)
Other comprehensive income	16,253	23,011	41,542	48,202
Ending balance	$ 23,134	$ (9,972)	$ 23,134	$ (9,972)