Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	$ 2,928,787	$ 3,262,586
Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	2,928,787	3,262,586
Residential Held-for-sale, Fair Value Disclosure	366,330	136,280
Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Trading assets	12,454	2,527
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	10,972	710
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Other Debt And Other Equity Securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,618	1,646
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | GNMA
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	823,787	985,139
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | FFELP asset backed securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	341,424	263,693
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Debt And Other Equity Securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	3,000	3,000
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Available-for-sale Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	2,928,787	3,262,586
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Residential loans held for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	366,330	136,280
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Interest rate-related instruments — customer and mirror, net
Assets, Fair Value Disclosure [Abstract]
Trading assets	220,445	77,024
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	30,449	13,073
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Foreign currency exchange forwards
Assets, Fair Value Disclosure [Abstract]
Trading assets	9,272	4,226
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	9,215	4,048
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading assets	69,241	20,528
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	67,592	19,624
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Mortgage banking(a)
Assets, Fair Value Disclosure [Abstract]
Trading assets	12,454	2,527
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Forward commitments (mortgage)
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	10,972	710
FNMA / FHLMC | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | FNMA / FHLMC
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	104,485	132,660
FNMA / FHLMC | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commercial mortgage-related securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	22,773	21,728
GNMA | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commercial mortgage-related securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	1,114,443	1,310,207
Obligations of state and political subdivisions (municipal securities)
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	508,636	546,160
Obligations of state and political subdivisions (municipal securities) | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	508,636	546,160
U.S. government SBA agency securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	10,238
U.S. government SBA agency securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	$ 10,238	$ 0