Fair Value Disclosures - Schedule of Estimated Fair Values and Carrying Values of All Financial Instruments (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	$ 222,464,000	$ 224,875,000	$ 281,354,000
FEDERAL FUNDS SOLD	12,300,000	0	0
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	365,397,000	221,336,000	255,237,000
Available-for-sale securities	4,658,526,000	5,298,557,000	4,732,762,000
Loans held-for-investment, net allowance for credit losses	7,139,848,000	6,495,397,000	7,060,057,000
Loans held for sale	16,109,000	11,996,000	14,253,000
Borrowings	26,803,000	24,628,000	22,153,000
IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	803,000	827,000	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	0	0
Forward mortgage-backed securities trades asset (liability)	91,000	334,000	288,000
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)	(91,000)	(334,000)	(288,000)
Carrying Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	222,464,000	224,875,000	281,354,000
FEDERAL FUNDS SOLD	12,300,000	0	0
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	365,397,000	221,336,000	255,237,000
Deposits with no stated maturities	10,351,267,000	10,196,920,000	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	16,109,000	11,996,000	14,253,000
Accrued interest receivable	56,278,000	50,658,000	58,544,000
Deposits with stated maturities	938,541,000	739,498,000	938,980,000
Repurchase Agreements	307,297,000	608,299,000	381,928,000
Borrowings	26,803,000	24,628,000	22,153,000
Accrued interest payable	8,362,000	3,617,000	10,215,000
Carrying Value [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	803,000	827,000	427,000
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)	(91,000)	(334,000)	(288,000)
Carrying Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	4,658,526,000	5,298,557,000	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 allowance for credit losses	7,139,847,000	6,495,397,000	7,060,057,000
Estimated Fair Value [Member] | Level 1 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and due from banks	222,464,000	224,875,000	281,354,000
FEDERAL FUNDS SOLD	12,300,000	0	0
INTEREST-BEARING DEMAND DEPOSITS IN BANKS	365,397,000	221,336,000	255,237,000
Deposits with no stated maturities	10,351,267,000	10,196,920,000	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	16,109,000	12,018,000	14,378,000
Accrued interest receivable	56,278,000	50,658,000	58,544,000
Deposits with stated maturities	938,459,000	736,434,000	938,534,000
Repurchase Agreements	307,297,000	608,299,000	381,928,000
Borrowings	26,803,000	24,628,000	22,153,000
Accrued interest payable	8,362,000	3,617,000	10,215,000
Estimated Fair Value [Member] | Level 2 Inputs [Member] | IRLCs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
IRLCs	803,000	827,000	427,000
Estimated Fair Value [Member] | Levels 1 and 2 Inputs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Available-for-sale securities	4,658,526,000	5,298,557,000	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 allowance for credit losses	$ 7,141,043,000	$ 6,464,027,000	$ 7,036,722,000