Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	$ 3,356,949	$ 3,085,441
Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	53,693	26,531
Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	3,303,257	3,058,910
Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Trading assets	4,255	0
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	0	2,046
Fair Value, Inputs, Level 3 | Forward commitments (mortgage)
Assets, Fair Value Disclosure [Abstract]
Trading assets	4,255	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Other Debt And Other Equity Securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	1,684	1,661
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Total investment securities AFS
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	53,693	26,531
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | SBA
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		8,584
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | FFELP
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	325,933	327,189
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Debt And Other Equity Securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	3,000	3,000
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Total investment securities AFS
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	3,303,257	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	153,151	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	121,020	192,518
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	28,382	25,680
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Foreign currency exchange forwards
Assets, Fair Value Disclosure [Abstract]
Trading assets	3,044	4,909
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	2,828	4,836
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading assets	5,808	12,486
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	5,098	11,155
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Mortgage banking(a)(b)
Assets, Fair Value Disclosure [Abstract]
Trading assets	6,917	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	94,349	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	1,910,954	1,461,241
GNMA [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commercial mortgage-related securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	389,411	524,756
GNMA [Member] | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Residential Related Securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	123,365	235,537
US Treasury Securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities		26,531
US Treasury Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	53,693	26,531
Obligations of state and political subdivisions (municipal securities)
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	433,182	450,662
Obligations of state and political subdivisions (municipal securities) | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	433,182	450,662
Agency Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	14,904	25,038
SBA
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	8,160
SBA | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	$ 8,160	$ 8,584