Loans - Investment in Loans Related to Allowance for Loan Losses by Portfolio Segment Disaggregated Based on Impairment Methodology (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 16,736,026	$ 16,336,397
Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	5,539,277	5,364,954
Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	987,925	1,077,792
Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	91,919	428,882
Commercial Real Estate Buildings Land And Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	6,520,280	6,272,339
Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,535,808	1,304,271
Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	1,561,035	1,410,790
Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	499,782	477,369
Specific Valuation Allowances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Specific Allocations	11,095	16,452
Specific Valuation Allowances [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Specific Allocations	3,360	10,536
Specific Valuation Allowances [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Specific Allocations	6,172	5,480
Specific Valuation Allowances [Member] | Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Specific Allocations	0	0
Specific Valuation Allowances [Member] | Commercial Real Estate Buildings Land And Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Specific Allocations	1,481	200
Specific Valuation Allowances [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Specific Allocations	0	200
Specific Valuation Allowances [Member] | Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Specific Allocations	82	36
Specific Valuation Allowances [Member] | Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Specific Allocations	0	0
Loans Individually Evaluated for Impairment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	50,584	66,837
Loans Individually Evaluated for Impairment [Member] | Commercial Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	12,539	24,523
Loans Individually Evaluated for Impairment [Member] | Commercial and Industrial Total Energy Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	15,906	16,393
Loans Individually Evaluated for Impairment [Member] | Paycheck Protection Program [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	0
Loans Individually Evaluated for Impairment [Member] | Commercial Real Estate Buildings Land And Other Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	21,205	24,670
Loans Individually Evaluated for Impairment [Member] | Construction Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	0	948
Loans Individually Evaluated for Impairment [Member] | Total consumer real estate loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	934	303
Loans Individually Evaluated for Impairment [Member] | Consumer Loan [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Net of Deferred Income	$ 0	$ 0