Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($)	9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 296,188,000	$ 208,277,000	$ 281,354,000
Interest-bearing demand deposits in banks	287,476,000	180,008,000	255,237,000
Estimated Fair Value	4,612,299,000	4,652,537,000	4,732,762,000
Loans held-for-investment, net of allowance for credit losses	7,623,255,000	6,904,982,000	7,060,057,000
Loans held for sale	20,114,000	12,229,000	14,253,000
Borrowings	25,978,000	129,753,000	22,153,000
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	499,000	409,000	427,000
Forward mortgage-backed securities trades asset (liability)	0	0	0
Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	0	237,000	0
Forward mortgage-backed securities trades asset (liability)	98,000	0	288,000
Carrying Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	296,188,000	208,277,000	281,354,000
Interest-bearing demand deposits in banks	287,476,000	180,008,000	255,237,000
Deposits with no stated maturities	10,746,194,000	9,712,296,000	10,199,320,000
Carrying Value [Member] | Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	20,114,000	12,229,000	14,253,000
Accrued interest receivable	56,427,000	53,518,000	58,544,000
Deposits with stated maturities	1,009,667,000	1,004,227,000	938,980,000
Repurchase Agreements	57,557,000	621,791,000	381,928,000
Borrowings	25,978,000	129,753,000	22,153,000
Accrued interest payable	9,502,000	13,557,000	10,215,000
Carrying Value [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades asset (liability)	(98,000)	237,000	(288,000)
Carrying Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value	4,612,299,000	4,652,537,000	4,732,762,000
Carrying Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net of allowance for credit losses	7,623,255,000	6,904,982,000	7,060,057,000
Carrying Value [Member] | Level 3 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	499,000	409,000	427,000
Estimated Fair Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	296,188,000	208,277,000	281,354,000
Interest-bearing demand deposits in banks	287,476,000	180,008,000	255,237,000
Deposits with no stated maturities	10,746,194,000	9,712,296,000	10,199,320,000
Estimated Fair Value [Member] | Level 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held for sale	20,293,000	12,266,000	14,378,000
Accrued interest receivable	56,427,000	53,518,000	58,544,000
Deposits with stated maturities	1,011,199,000	1,002,893,000	938,534,000
Repurchase Agreements	57,557,000	621,791,000	381,928,000
Borrowings	25,978,000	129,753,000	22,153,000
Accrued interest payable	9,502,000	13,557,000	10,215,000
Estimated Fair Value [Member] | Level 2 Inputs [Member] | Forward Mortgage-Backed Securities Trades [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Forward mortgage-backed securities trades asset (liability)	(98,000)	237,000	(288,000)
Estimated Fair Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Estimated Fair Value	4,612,299,000	4,652,537,000	4,732,762,000
Estimated Fair Value [Member] | Level 3 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans held-for-investment, net of allowance for credit losses	7,607,920,000	6,890,218,000	7,036,722,000
Estimated Fair Value [Member] | Level 3 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	$ 499,000	$ 409,000	$ 427,000