FAIR VALUE - Fair Value (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Assets:
Investment securities available for sale	$ 5,175,803		$ 5,599,520
Held To Maturity Securities Amortized	359,169		437,537
Less: allowance for credit losses on held to maturity securities	(2,250)		(8,286)
Loans held for investment, net of ACL	11,687,317		11,292,361
Mortgage servicing rights	27,601	$ 28,034	29,037	$ 29,690	$ 30,277	$ 30,986
Advances from the FHLB:
Short-term	0		475,000
Long-term	500,000		200,000
Other long-term borrowings	161,700		183,762
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	584,913		480,505
Investment securities available for sale	5,175,803		5,599,520
Held To Maturity Securities Amortized	359,169		437,537
Less: allowance for credit losses on held to maturity securities	(2,250)		(8,286)
Investment securities held to maturity, net of ACL	356,919		429,251
Equity securities	43,908		50,428
Other investment securities	4,775		4,861
Loans held for sale	8,961		12,306
Total gross loans held for investment portfolio	11,950,932		11,552,825
ACL for loans and finance leases	(263,615)		(260,464)
Loans held for investment, net of ACL	11,687,317		11,292,361
Mortgage servicing rights	27,601		29,037
Derivative Assets	360		633
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,435,237		16,143,467
Short-term securities sold under agreements to repurchase (amortized cost)			75,133
Advances from the FHLB:
Short-term			475,000
Long-term	500,000		200,000
Other long-term borrowings	161,700		183,762
Derivative Liabilities	170		476
Federal Home Loan Bank Stock	34,600		42,900
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	584,913		480,505
Investment securities available for sale	5,175,803		5,599,520
Investment securities held to maturity, net of ACL	342,851		427,115
Equity securities	43,908		50,428
Other investment securities	4,775		4,861
Loans held for sale	8,961		12,306
Loans held for investment, net of ACL	11,566,106		11,106,809
Mortgage servicing rights	45,114		44,710
Derivative Assets	360		633
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,447,189		16,139,937
Short-term securities sold under agreements to repurchase (amortized cost)			75,230
Advances from the FHLB:
Short-term			474,731
Long-term	491,505		199,865
Other long-term borrowings	159,549		187,246
Derivative Liabilities	170		476
Estimate Of Fair Value Fair Value Disclosure [Member] | Fair Value Inputs Level 1 [Member]
Assets:
Cash and due from banks and money market investments	584,913		480,505
Investment securities available for sale	140,723		138,875
Investment securities held to maturity, net of ACL	0		0
Equity securities	0		0
Other investment securities	4,775		4,861
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
Short-term securities sold under agreements to repurchase (amortized cost)			0
Advances from the FHLB:
Short-term			0
Long-term	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
Investment securities available for sale	5,028,714		5,452,150
Investment securities held to maturity, net of ACL	232,719		260,106
Equity securities	43,908		50,428
Other investment securities	0		0
Loans held for sale	8,961		12,306
Loans held for investment, net of ACL	0		0
Mortgage servicing rights	0		0
Derivative Assets	360		633
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,447,189		16,139,937
Short-term securities sold under agreements to repurchase (amortized cost)			75,230
Advances from the FHLB:
Short-term			474,731
Long-term	491,505		199,865
Other long-term borrowings	0		0
Derivative Liabilities	170		476
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
Investment securities available for sale	6,366		8,495
Investment securities held to maturity, net of ACL	110,132		167,009
Equity securities	0		0
Other investment securities	0		0
Loans held for sale	0		0
Loans held for investment, net of ACL	11,566,106		11,106,809
Mortgage servicing rights	45,114		44,710
Derivative Assets	0		0
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	0		0
Short-term securities sold under agreements to repurchase (amortized cost)			0
Advances from the FHLB:
Short-term			0
Long-term	0		0
Other long-term borrowings	159,549		187,246
Derivative Liabilities	$ 0		$ 0