Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($)	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 255,018,000	$ 293,286,000	$ 242,665,000
Interest-bearing demand deposits in bank	23,839,000	37,392,000	222,899,000
Securities available-for-sale, Estimated Fair Value	5,066,262,000	5,474,359,000	6,215,036,000
Loans held-for-investment, net allowance for credit losses	6,691,029,000	6,366,034,000	5,806,650,000
Loans held for sale	19,220,000	11,965,000	26,445,000
Borrowings	587,656,000	642,507,000	768,364,000
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	455,000	400,000	1,414,000
Liability Derivative Fair Value	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value	160,000	85,000	58,000
Liability Derivative Fair Value	0	0	0
Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Accrued interest payable	8,155,000
Carrying Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	255,018,000	293,286,000	242,665,000
Interest-bearing demand deposits in bank	23,839,000	37,392,000	222,899,000
Deposits with no stated maturities	9,914,131,000	10,480,841,000	10,681,596,000
Carrying Value [Member] | Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	19,220,000	11,965,000	26,445,000
Accrued interest receivable	56,236,000	58,162,000	58,047,000
Deposits with stated maturities		524,666,000	441,387,000
Borrowings	587,656,000	642,507,000	768,364,000
Accrued interest payable		1,121,000	423,000
Asset Derivative Fair Value	455,000
Liability Derivative Fair Value	160,000
Carrying Value [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value		400,000	1,414,000
Carrying Value [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability Derivative Fair Value		85,000	58,000
Carrying Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, Estimated Fair Value	5,066,262,000	5,474,359,000	6,215,036,000
Carrying Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net allowance for credit losses	6,691,029,000	6,366,034,000	5,806,650,000
Deposits with no stated maturities	893,429,000
Estimated Fair Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	255,018,000	293,286,000	242,665,000
Interest-bearing demand deposits in bank	23,839,000	37,392,000	222,899,000
Deposits with no stated maturities	9,914,131,000	10,480,841,000	10,681,596,000
Estimated Fair Value [Member] | Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	19,264,000	11,965,000	26,445,000
Accrued interest receivable	56,236,000	58,162,000	58,047,000
Deposits with stated maturities		518,811,000	439,546,000
Borrowings	587,656,000	642,507,000	768,364,000
Accrued interest payable	8,155,000	1,121,000	423,000
Asset Derivative Fair Value	455,000
Liability Derivative Fair Value	160,000
Estimated Fair Value [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset Derivative Fair Value		400,000	1,414,000
Estimated Fair Value [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liability Derivative Fair Value		85,000	58,000
Estimated Fair Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities available-for-sale, Estimated Fair Value	5,066,262,000	5,474,359,000	6,215,036,000
Estimated Fair Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net allowance for credit losses	6,672,348,000	$ 6,372,859,000	$ 5,852,415,000
Deposits with stated maturities	$ 891,181,000