FAIR VALUE - Estimated Fair Value and Carrying Value of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Assets:
Available-for-sale debt securities (fair value)	$ 4,565,302	$ 5,229,984
Held To Maturity Securities Amortized	317,786	354,178
Less: allowance for credit losses on held to maturity securities	(802)	(2,197)
Loans held for investment	12,746,556	12,185,483
Allowance for loan and lease losses	(243,942)	(261,843)	$ (260,464)	$ (269,030)
Loans held for investment, net of ACL	12,502,614	11,923,640
Mortgage servicing rights	25,019	26,941	$ 29,037	$ 30,986
Advances from the FHLB:
Junior subordinated debentures (amortized cost)	61,700	161,700
Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	1,159,415	663,164
Available-for-sale debt securities (fair value)	4,565,302	5,229,984
Held To Maturity Securities Amortized	317,786	354,178
Less: allowance for credit losses on held to maturity securities	(802)	(2,197)
Investment securities held to maturity, net of ACL	316,984	351,981
Equity securities (amortized cost)	47,132	44,782
Other equity securities	4,886	4,893
Loans held for sale	15,276	7,368
Loans held for investment	12,746,556	12,185,483
Allowance for loan and lease losses	(243,942)	(261,843)
Loans held for investment, net of ACL	12,502,614	11,923,640
Mortgage servicing rights	25,019	26,941
Derivative Assets	318	341
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,871,298	16,555,985
Advances from the FHLB:
Long-term advances from the FHLB	500,000	500,000
Junior subordinated debentures (amortized cost)	61,700	161,700
Derivative Liabilities	150	317
Federal Home Loan Bank Stock	34,000	34,600
Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and due from banks and money market investments	1,159,415	663,164
Available-for-sale debt securities (fair value)	4,565,302	5,229,984
Investment securities held to maturity, net of ACL	308,040	346,132
Equity securities (amortized cost)	47,132	44,782
Other equity securities	4,886	4,893
Loans held for sale	15,276	7,476
Loans held for investment, net of ACL	12,406,405	11,762,855
Mortgage servicing rights	43,046	45,244
Derivative Assets	318	341
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,872,963	16,565,435
Advances from the FHLB:
Long-term advances from the FHLB	500,128	500,522
Junior subordinated debentures (amortized cost)	61,752	159,999
Derivative Liabilities	150	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	1,159,415	663,164
Available-for-sale debt securities (fair value)	59,189	135,393
Investment securities held to maturity, net of ACL	0	0
Equity securities (amortized cost)	0	0
Other equity securities	4,886	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
Junior subordinated debentures (amortized cost)	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 (fair value)	4,499,298	5,088,391
Investment securities held to maturity, net of ACL	212,432	235,239
Equity securities (amortized cost)	47,132	44,782
Other equity securities	0	0
Loans held for sale	15,276	7,476
Loans held for investment, net of ACL	0	0
Mortgage servicing rights	0	0
Derivative Assets	318	341
Financial Instruments Financial Liabilities Balance Sheet Groupings [Abstract]
Deposits	16,872,963	16,565,435
Advances from the FHLB:
Long-term advances from the FHLB	500,128	500,522
Junior subordinated debentures (amortized cost)	0	0
Derivative Liabilities	150	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 (fair value)	6,815	6,200
Investment securities held to maturity, net of ACL	95,608	110,893
Equity securities (amortized cost)	0	0
Other equity securities	0	0
Loans held for sale	0	0
Loans held for investment, net of ACL	12,406,405	11,762,855
Mortgage servicing rights	43,046	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
Junior subordinated debentures (amortized cost)	61,752	159,999
Derivative Liabilities	$ 0	$ 0