Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	$ 3,893,379	$ 3,085,441
Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	123,981	26,531
Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	3,769,399	3,058,910
Fair Value, Inputs, Level 3
Assets, Fair Value Disclosure [Abstract]
Trading assets	972	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	972	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Available-for-sale Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	123,981	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	4,109	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	212,797	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	7,179	8,584
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Debt securities
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	2,999	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	3,769,399	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	158,202	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	110,898	192,518
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	24,322	25,680
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Foreign currency exchange forwards
Assets, Fair Value Disclosure [Abstract]
Trading assets	4,637	4,909
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	4,454	4,836
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Commodity contracts
Assets, Fair Value Disclosure [Abstract]
Trading assets	6,546	12,486
Liabilities, Fair Value Disclosure [Abstract]
Trading liabilities	6,471	11,155
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Residential Related Securities | Private-label Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	76,033	0
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Mortgage banking(a)(b)
Assets, Fair Value Disclosure [Abstract]
Trading assets	5,187
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Interest Rate Lock Commitments and Forward Commitments Total
Assets, Fair Value Disclosure [Abstract]
Trading assets	6,159	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	353,175	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	2,377,408	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	231,096	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	79,696	235,537
US Treasury Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	123,981	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	414,020	450,662
Agency Securities | Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	14,998	25,038
US Government-sponsored Enterprises Debt Securities [Member]
Assets, Fair Value Disclosure [Abstract]
Available-for-sale Securities	$ 7,179
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