Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 5,547,548	$ 4,987,243	$ 5,269,175	$ 5,017,617
Other comprehensive (loss) income	(42,879)	10,180	(101,893)	51,722
Ending balance	5,690,201	5,126,106	5,690,201	5,126,106
AFS Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(8,152)	42,850	52,247	(2,419)
Net unrealized gains arising during the period	(40,928)	5,126	(100,747)	58,262
Amounts reclassified from AOCI	(250)	(492)	(830)	(8,359)
Other comprehensive (loss) income	(41,178)	4,634	(101,577)	49,903
Ending balance	(49,330)	47,484	(49,330)	47,484
Cash Flow Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(730)	(1,333)	(1,230)	0
Net unrealized gains arising during the period	(121)	25	108	(1,038)
Amounts reclassified from AOCI	172	62	443	(208)
Other comprehensive (loss) income	51	87	551	(1,246)
Ending balance	(679)	(1,246)	(679)	(1,246)
Foreign Currency Translation Adjustments, Net of Hedges
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5,807)	(18,383)	(6,692)	(15,989)
Net unrealized gains arising during the period	(1,752)	5,459	(867)	3,065
Amounts reclassified from AOCI	0	0	0	0
Other comprehensive (loss) income	(1,752)	5,459	(867)	3,065
Ending balance	(7,559)	(12,924)	(7,559)	(12,924)
AOCI, Net of Tax
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(14,689)	23,134	44,325	(18,408)
Net unrealized gains arising during the period	(42,801)	10,610	(101,506)	60,289
Amounts reclassified from AOCI	(78)	(430)	(387)	(8,567)
Other comprehensive (loss) income	(42,879)	10,180	(101,893)	51,722
Ending balance	$ (57,568)	$ 33,314	$ (57,568)	$ 33,314