Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 5,285,027	$ 4,902,985	$ 5,269,175	$ 5,017,617
Other comprehensive income (loss)	75,351	16,253	(59,014)	41,542
Ending balance	5,547,548	4,987,243	5,547,548	4,987,243
AFS Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(81,201)	25,034	52,247	(2,419)
Net unrealized gains (losses) arising during the period	73,494	24,606	(59,819)	53,136
Amounts reclassified from AOCI	(445)	(6,790)	(580)	(7,867)
Other comprehensive income (loss)	73,049	17,816	(60,399)	45,269
Ending balance	(8,152)	42,850	(8,152)	42,850
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(798)	0	(1,230)	0
Net unrealized gains (losses) arising during the period	(76)	(1,063)	229	(1,063)
Amounts reclassified from AOCI	144	(270)	271	(270)
Other comprehensive income (loss)	68	(1,333)	500	(1,333)
Ending balance	(730)	(1,333)	(730)	(1,333)
Foreign Currency Translation Adjustments, Net of Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(8,041)	(18,153)	(6,692)	(15,989)
Net unrealized gains (losses) arising during the period	2,234	(230)	885	(2,394)
Amounts reclassified from AOCI	0	0	0	0
Other comprehensive income (loss)	2,234	(230)	885	(2,394)
Ending balance	(5,807)	(18,383)	(5,807)	(18,383)
AOCI, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(90,040)	6,881	44,325	(18,408)
Net unrealized gains (losses) arising during the period	75,652	23,313	(58,705)	49,679
Amounts reclassified from AOCI	(301)	(7,060)	(309)	(8,137)
Other comprehensive income (loss)	75,351	16,253	(59,014)	41,542
Ending balance	$ (14,689)	$ 23,134	$ (14,689)	$ 23,134