Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Thousands			12 Months Ended
		Jan. 01, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		$ 3,841,951	$ 5,017,617	$ 4,423,974	$ 3,841,951
Net unrealized gains (losses) arising during the period			71,477	42,534	(12,598)
Amount reclassified from AOCI			(8,744)	(2,768)	(1,786)
Other comprehensive income (loss)			62,733	39,766	(14,384)
Ending balance			5,269,175	5,017,617	4,423,974
AFS Debt Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(30,898)	(2,419)	(45,821)	(30,898)
Net unrealized gains (losses) arising during the period			63,329	46,170	(6,866)
Amount reclassified from AOCI			(8,663)	(2,768)	(1,786)
Other comprehensive income (loss)			54,666	43,402	(8,652)
Ending balance			52,247	(2,419)	(45,821)
AFS Debt Securities | Cumulative Effect, Period of Adoption, Adjusted Balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		(37,169)
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			(1,149)	0	0
Amount reclassified from AOCI			(81)	0	0
Other comprehensive income (loss)			(1,230)	0	0
Ending balance			(1,230)	0	0
Cash Flow Hedges | Cumulative Effect, Period of Adoption, Adjusted Balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		0
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(6,621)	(15,989)	(12,353)	(6,621)
Net unrealized gains (losses) arising during the period			9,297	(3,636)	(5,732)
Amount reclassified from AOCI			0	0	0
Other comprehensive income (loss)			9,297	(3,636)	(5,732)
Ending balance			(6,692)	(15,989)	(12,353)
Foreign Currency Translation Adjustments | Cumulative Effect, Period of Adoption, Adjusted Balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		(6,621)
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance		(37,519)	(18,408)	(58,174)	(37,519)
Other comprehensive income (loss)			62,733	39,766	(14,384)
Ending balance			$ 44,325	$ (18,408)	(58,174)
Total | Cumulative Effect, Period of Adoption, Adjusted Balance
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		(43,790)
Accounting Standards Update 2016-01 | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	(160)			(160)
Accounting Standards Update 2016-01 | AFS Debt Securities | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		385
Accounting Standards Update 2016-01 | Cash Flow Hedges | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		0
Accounting Standards Update 2016-01 | Foreign Currency Translation Adjustments | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Ending balance		0
Accounting Standards Update 2016-01 | Total | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	[1]	385			385
Ending balance		385
Accounting Standards Update 2018-02
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		(6,700)
Accounting Standards Update 2018-02 | AFS Debt Securities | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		(6,656)
Accounting Standards Update 2018-02 | Cash Flow Hedges | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		0
Accounting Standards Update 2018-02 | Foreign Currency Translation Adjustments | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		0
Accounting Standards Update 2018-02 | Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate	[2]				$ 6,656
Accounting Standards Update 2018-02 | Total | Cumulative Effect, Period of Adoption, Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification of tax effects in AOCI resulting from the new federal corporate income tax rate		$ (6,656)

[1] Represents the impact of the adoption of Accounting Standards Update (“ASU”) 2016-01, Financial Instruments — Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities on January 1, 2018.

[2] Represents amounts reclassified from AOCI to retained earnings due to the early adoption of ASU 2018-02, Income Statement — Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income on January 1, 2018.