FAIR VALUE - Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Assets:
Available-for-sale debt securities, at fair value (amortized cost of $5,695,485 as of March 31, 2024 and $5,863,294 as of December 31, 2023; ACL of $442 as of March 31, 2024 and $511 as of December 31, 2023)	$ 5,047,179	$ 5,229,984
Held To Maturity Securities Amortized	349,330	354,178
Less: allowance for credit losses on held to maturity securities	(1,235)	(2,197)
Loans held for investment	12,311,448	12,185,483
Allowance for loan and lease losses	(263,592)	(261,843)	$ (265,567)	$ (260,464)
Loans held for investment, net of ACL	12,047,856	11,923,640
Mortgage servicing rights	26,355	26,941	$ 28,431	$ 29,037
Advances from the FHLB:
Long-term advances from the FHLB	500,000	500,000
Other long-term borrowings	161,700	161,700
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	684,519	663,164
Available-for-sale debt securities, at fair value (amortized cost of $5,695,485 as of March 31, 2024 and $5,863,294 as of December 31, 2023; ACL of $442 as of March 31, 2024 and $511 as of December 31, 2023)	5,047,179	5,229,984
Held To Maturity Securities Amortized	349,330	354,178
Less: allowance for credit losses on held to maturity securities	(1,235)	(2,197)
Investment securities held to maturity, net of ACL	348,095	351,981
Equity securities	46,519	44,782
Other investment securities	4,871	4,893
Loans held for sale	12,080	7,368
Loans held for investment	12,311,448	12,185,483
Allowance for loan and lease losses	(263,592)	(261,843)
Loans held for investment, net of ACL	12,047,856	11,923,640
Mortgage servicing rights	26,355	26,941
Derivative Assets	239	341
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,545,511	16,555,985
Advances from the FHLB:
Long-term advances from the FHLB	500,000	500,000
Other long-term borrowings	161,700	161,700
Derivative Liabilities	242	317
Federal Home Loan Bank Stock	34,600	34,600
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	684,519	663,164
Available-for-sale debt securities, at fair value (amortized cost of $5,695,485 as of March 31, 2024 and $5,863,294 as of December 31, 2023; ACL of $442 as of March 31, 2024 and $511 as of December 31, 2023)	5,047,179	5,229,984
Investment securities held to maturity, net of ACL	338,120	346,132
Equity securities	46,519	44,782
Other investment securities	4,871	4,893
Loans held for sale	12,173	7,476
Loans held for investment, net of ACL	11,953,468	11,762,855
Mortgage servicing rights	44,764	45,244
Derivative Assets	239	341
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,546,891	16,565,435
Advances from the FHLB:
Long-term advances from the FHLB	496,672	500,522
Other long-term borrowings	160,199	159,999
Derivative Liabilities	242	317
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Assets:
Cash and due from banks and money market investments	684,519	663,164
Available-for-sale debt securities, at fair value (amortized cost of $5,695,485 as of March 31, 2024 and $5,863,294 as of December 31, 2023; ACL of $442 as of March 31, 2024 and $511 as of December 31, 2023)	116,068	135,393
Investment securities held to maturity, net of ACL	0	0
Equity securities	0	0
Other investment securities	4,871	4,893
Loans held for sale	0	0
Loans held for investment, net of ACL	0	0
Mortgage servicing rights	0	0
Derivative Assets	0	0
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	0	0
Advances from the FHLB:
Long-term advances from the FHLB	0	0
Other long-term borrowings	0	0
Derivative Liabilities	0	0
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 2 [Member]
Assets:
Cash and due from banks and money market investments	0	0
Available-for-sale debt securities, at fair value (amortized cost of $5,695,485 as of March 31, 2024 and $5,863,294 as of December 31, 2023; ACL of $442 as of March 31, 2024 and $511 as of December 31, 2023)	4,924,836	5,088,391
Investment securities held to maturity, net of ACL	228,237	235,239
Equity securities	46,519	44,782
Other investment securities	0	0
Loans held for sale	12,173	7,476
Loans held for investment, net of ACL	0	0
Mortgage servicing rights	0	0
Derivative Assets	239	341
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,546,891	16,565,435
Advances from the FHLB:
Long-term advances from the FHLB	496,672	500,522
Other long-term borrowings	0	0
Derivative Liabilities	242	317
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 3 [Member]
Assets:
Cash and due from banks and money market investments	0	0
Available-for-sale debt securities, at fair value (amortized cost of $5,695,485 as of March 31, 2024 and $5,863,294 as of December 31, 2023; ACL of $442 as of March 31, 2024 and $511 as of December 31, 2023)	6,275	6,200
Investment securities held to maturity, net of ACL	109,883	110,893
Equity securities	0	0
Other investment securities	0	0
Loans held for sale	0	0
Loans held for investment, net of ACL	11,953,468	11,762,855
Mortgage servicing rights	44,764	45,244
Derivative Assets	0	0
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	0	0
Advances from the FHLB:
Long-term advances from the FHLB	0	0
Other long-term borrowings	160,199	159,999
Derivative Liabilities	$ 0	$ 0