Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	$ 3,149,773	$ 3,262,586
Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	26,735	0
Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	3,123,039	3,262,586
Residential Held-for-sale, Fair Value Disclosure	196,673	136,280
Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Trading assets	12,837	2,527
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	1,293	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	1,647	1,646
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Total investment securities available for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	26,735	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | GNMA
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	605,561	985,139
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | FFELP
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	340,474	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 | Total investment securities available for sale
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	3,123,039	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	196,673	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	238,003	77,024
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	31,472	13,073
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Foreign currency exchange forwards
Assets, Fair Value Disclosure [Abstract]
Trading assets	4,200	4,226
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	4,102	4,048
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading assets	38,543	20,528
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	36,998	19,624
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Mortgage banking(a)
Assets, Fair Value Disclosure [Abstract]
Trading assets	12,837	2,527
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Forward commitments (mortgage)
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	1,293	710
FNMA / FHLMC | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | FNMA / FHLMC
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	818,110	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	22,061	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	803,362	1,310,207
US Treasury Securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	26,735
US Treasury Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	26,735	0
Obligations of state and political subdivisions (municipal securities)
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	495,888	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	495,888	546,160
Agency Securities
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	25,007
Agency Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	25,007	0
SBA
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	9,575
SBA | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Investment securities available for sale	$ 9,575	$ 0