Fair Value Measurements - Estimated Fair Values and Related Carrying Amounts of Financial Instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Held-to-maturity securities	$ 1,487,916	$ 341,925
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,781,413	3,472,152
Interest bearing balances due from banks - time	1,780	1,579
Held-to-maturity securities	1,516,797	333,031
Interest receivable	68,405	72,597
Loans, net	10,622,719	12,662,847
Federal funds purchased and securities sold under agreements to repurchase	217,276	299,111
Other borrowings	1,338,585	1,342,067
Subordinated notes and debentures	383,278	382,874
Interest payable	11,230	8,887
Carrying Amount | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	4,918,845	4,482,091
Carrying Amount | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	10,697,451	9,672,608
Carrying Amount | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	2,455,774	2,832,327
Fair Value Measurements
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,781,413	3,472,152
Interest bearing balances due from banks - time	1,780	1,579
Held-to-maturity securities	1,487,916	341,925
Interest receivable	68,405	72,597
Loans, net	10,705,185	12,736,991
Federal funds purchased and securities sold under agreements to repurchase	217,276	299,111
Other borrowings	1,408,087	1,448,625
Subordinated notes and debentures	395,786	398,827
Interest payable	11,230	8,887
Fair Value Measurements | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	4,918,845	4,482,091
Fair Value Measurements | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	10,697,451	9,672,608
Fair Value Measurements | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	2,460,441	2,848,621
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	1,781,413	3,472,152
Interest bearing balances due from banks - time	0	0
Held-to-maturity securities	0	0
Interest receivable	0	0
Loans, net	0	0
Federal funds purchased and securities sold under agreements to repurchase	0	0
Other borrowings	0	0
Subordinated notes and debentures	0	0
Interest payable	0	0
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1) | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1) | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Quoted Prices in Active Markets for Identical Assets (Level 1) | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Significant Other Observable Inputs (Level 2)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Interest bearing balances due from banks - time	1,780	1,579
Held-to-maturity securities	1,487,916	341,925
Interest receivable	68,405	72,597
Loans, net	0	0
Federal funds purchased and securities sold under agreements to repurchase	217,276	299,111
Other borrowings	1,408,087	1,448,625
Subordinated notes and debentures	395,786	398,827
Interest payable	11,230	8,887
Fair Value Measurements | Significant Other Observable Inputs (Level 2) | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	4,918,845	4,482,091
Fair Value Measurements | Significant Other Observable Inputs (Level 2) | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	10,697,451	9,672,608
Fair Value Measurements | Significant Other Observable Inputs (Level 2) | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Significant Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Interest bearing balances due from banks - time	0	0
Held-to-maturity securities	0	0
Interest receivable	0	0
Loans, net	10,705,185	12,736,991
Federal funds purchased and securities sold under agreements to repurchase	0	0
Other borrowings	0	0
Subordinated notes and debentures	0	0
Interest payable	0	0
Fair Value Measurements | Significant Unobservable Inputs (Level 3) | Non-interest bearing transaction accounts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Significant Unobservable Inputs (Level 3) | Interest bearing transaction accounts and savings deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	0	0
Fair Value Measurements | Significant Unobservable Inputs (Level 3) | Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Deposits	$ 2,460,441	$ 2,848,621