Fair Value - Carrying Amounts and Estimated Fair Values of Financial Instruments, Not Carried at Fair Value (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, due from banks, money market,    and other interest-earning investments	$ 589,712	$ 276,337
Net loans	13,655,091	12,062,905
Accrued interest receivable	85,306	85,123
Noninterest-bearing demand deposits	5,633,672	4,042,286
Other time deposits	1,122,870
Brokered deposits	119,557	92,242
Federal funds purchased and interbank borrowings	1,166	350,414
Securities sold under agreements to repurchase	431,166	327,782
Federal Home Loan Bank advances	1,991,435	1,822,847
Other borrowings	252,787	243,685
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, due from banks, money market,    and other interest-earning investments	589,712	276,337
Accrued interest receivable	85,306	85,123
Noninterest-bearing demand deposits	5,633,672	4,042,286
Checking, NOW, savings, and money market    interest-bearing deposits	10,180,911	8,828,881
Other time deposits	1,103,313	1,589,988
Brokered deposits	119,557	92,242
Federal funds purchased and interbank borrowings	1,166	350,414
Securities sold under agreements to repurchase	431,166	327,782
Federal Home Loan Bank advances	1,991,435	1,822,847
Other borrowings	252,787	243,685
Accrued interest payable	5,443	8,272
Standby letters of credit	462	573
Commitments to extend credit	0	0
Carrying Value | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	3,922,642	2,867,711
Carrying Value | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	5,867,795	5,145,204
Carrying Value | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	2,235,814	2,331,990
Carrying Value | Consumer credit, net of unearned income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	1,628,840	1,718,000
Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, due from banks, money market,    and other interest-earning investments	589,712	276,337
Accrued interest receivable	21	15
Noninterest-bearing demand deposits	5,633,672	4,042,286
Checking, NOW, savings, and money market    interest-bearing deposits	10,180,911	8,828,881
Other time deposits	0	0
Brokered deposits	0	0
Federal funds purchased and interbank borrowings	1,166	350,414
Securities sold under agreements to repurchase	431,166	327,782
Federal Home Loan Bank advances	0	0
Other borrowings	0	0
Accrued interest payable	0	0
Standby letters of credit	0	0
Commitments to extend credit	0	0
Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	0	0
Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	0	0
Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1) | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	0	0
Estimate of Fair Value Measurement | Quoted Prices in Active Markets for Identical Assets (Level 1) | Consumer credit, net of unearned income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	0	0
Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, due from banks, money market,    and other interest-earning investments	0	0
Accrued interest receivable	27,977	28,185
Noninterest-bearing demand deposits	0	0
Checking, NOW, savings, and money market    interest-bearing deposits	0	0
Other time deposits	1,121,365	1,600,214
Brokered deposits	119,514	92,355
Federal funds purchased and interbank borrowings	0	0
Securities sold under agreements to repurchase	0	0
Federal Home Loan Bank advances	2,092,033	1,875,089
Other borrowings	254,612	254,519
Accrued interest payable	5,443	8,272
Standby letters of credit	0	0
Commitments to extend credit	0	0
Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2) | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	0	0
Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2) | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	0	0
Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2) | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	0	0
Estimate of Fair Value Measurement | Significant Other Observable Inputs (Level 2) | Consumer credit, net of unearned income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	0	0
Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash, due from banks, money market,    and other interest-earning investments	0	0
Accrued interest receivable	57,308	56,923
Noninterest-bearing demand deposits	0	0
Checking, NOW, savings, and money market    interest-bearing deposits	0	0
Other time deposits	0	0
Brokered deposits	0	0
Federal funds purchased and interbank borrowings	0	0
Securities sold under agreements to repurchase	0	0
Federal Home Loan Bank advances	0	0
Other borrowings	0	0
Accrued interest payable	0	0
Standby letters of credit	462	573
Commitments to extend credit	11,822	4,302
Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3) | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	3,912,948	2,831,298
Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3) | Commercial real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	5,797,447	5,130,848
Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3) | Residential real estate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	2,264,274	2,357,341
Estimate of Fair Value Measurement | Significant Unobservable Inputs (Level 3) | Consumer credit, net of unearned income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net loans	$ 1,618,365	$ 1,676,253