Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	$ 3,323,346	$ 3,085,441
Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	124,533	26,531
Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	3,198,813	3,058,910
Fair Value, Inputs, Level 3
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	430	2,046
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	124,533	26,531
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Other Debt And Other Equity Securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	3,187	1,661
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Federal Family Education Loan Program (FFELP) Guaranteed Loans [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	215,464	327,189
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | US Government-sponsored Enterprises Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	7,573	8,584
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Debt securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	3,000	3,000
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	3,198,813	3,058,910
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Residential loans held for sale
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	160,547	129,158
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Interest rate-related instruments — customer and mirror, net
Assets, Fair Value Disclosure [Abstract]
Trading assets	125,879	192,518
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	23,115	25,680
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Foreign currency exchange forwards
Assets, Fair Value Disclosure [Abstract]
Trading assets	3,747	4,909
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	3,556	4,836
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading assets	9,593	12,486
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	9,393	11,155
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Mortgage banking(a)
Assets, Fair Value Disclosure [Abstract]
Trading assets	6,543	9,624
FNMA / FHLMC | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commercial mortgage-related securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	95,708	22,904
FNMA / FHLMC | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Residential Related Securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	2,057,909	1,461,241
Government National Mortgage Association (GNMA) [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commercial mortgage-related securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	289,593	524,756
Government National Mortgage Association (GNMA) [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Residential Related Securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	93,967	235,537
US Treasury Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	124,533	26,531
US Treasury Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		26,531
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	420,609	450,662
Agency Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	14,991	25,038
US Government-sponsored Enterprises Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	$ 7,573
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		$ 8,584