Short and Long-term Funding, Composition (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Federal funds purchased	$ 7,070	$ 362,000
Securities sold under agreements to repurchase	185,901	71,097
Federal funds purchased and securities sold under agreements to repurchase	192,971	433,097
Commercial paper	59,346	32,016
Total short-term funding	252,317	465,113
Debt Instrument [Line Items]
Corporation subordinated notes, at par, due 2025	250,000	250,000
Finance Lease, Liability	1,128	2,209
Other Long-term Debt and Capitalized Costs	(1,663)	(2,866)
Other Long-term Debt	549,465	549,343
TotalShortTermLongTermExcludingFHLB	801,782	1,014,456
Advances from Federal Home Loan Banks [Abstract]
Short-term FHLB advances	0	520,000
Long-term FHLB advances	1,632,723	2,660,967
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	1,632,723	3,180,967
Debt, Long-term and Short-term, Combined Amount [Abstract]
Debt, Long-term and Short-term, Combined Amount, Total	2,434,505	4,195,422
Bank senior notes, at par, due 2021
Debt Instrument [Line Items]
Senior Notes	$ 300,000	$ 300,000