FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value By Balance Sheet Location) (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Assets:
Securities—trading	$ 25,268	$ 28,694
Securities—available-for-sale, net of allowance for credit losses of $750 and none, respectively; amortized cost $2,774,972 and $3,218,777, respectively	2,287,993	2,789,031
Securities—held-to-maturity	853,653	942,180
Securities purchased under agreements to resell	0	300,000
Liabilities:
FHLB advances at fair value	140,000	50,000
Subordinated notes, net	92,748	98,947
Reported Value Measurement [Member]
Assets:
Cash and cash equivalents	251,706	243,062
Securities—trading	25,268	28,694
Securities—available-for-sale, net of allowance for credit losses of $750 and none, respectively; amortized cost $2,774,972 and $3,218,777, respectively	2,287,993	2,789,031
Securities purchased under agreements to resell	0	300,000
Loans receivable held for sale	54,158	56,857
Loans receivable	10,464,457	10,005,259
Equity securities	552	553
FHLB stock	15,600	12,000
Bank-owned life insurance	303,347	297,565
Mortgage servicing rights	14,151	15,331
SBA servicing asset	717	835
Investments in limited partnerships	12,841	12,427
Liabilities:
Demand, interest checking and money market accounts	8,964,786	10,186,439
Regular savings	2,751,453	2,710,090
Certificates of deposit	1,458,313	723,530
FHLB advances at fair value	140,000	50,000
Other borrowings	188,440	232,799
Junior subordinated debentures at fair value	66,284	74,857
Estimate of Fair Value Measurement [Member]
Assets:
Cash and cash equivalents	251,706	243,062
Securities—trading	25,268	28,694
Securities—available-for-sale, net of allowance for credit losses of $750 and none, respectively; amortized cost $2,774,972 and $3,218,777, respectively	2,287,993	2,789,031
Securities purchased under agreements to resell	0	300,000
Loans receivable held for sale	54,213	56,948
Loans receivable	9,914,151	9,810,965
Equity securities	552	553
FHLB stock	15,600	12,000
Bank-owned life insurance	303,347	297,565
Mortgage servicing rights	36,469	35,148
SBA servicing asset	717	835
Investments in limited partnerships	12,841	12,427
Liabilities:
Demand, interest checking and money market accounts	8,964,786	10,186,439
Regular savings	2,751,453	2,710,090
Certificates of deposit	1,440,378	702,581
FHLB advances at fair value	140,000	50,000
Other borrowings	188,440	232,799
Subordinated notes, net	90,322	96,718
Junior subordinated debentures at fair value	66,284	74,857
Interest rate swaps [Member] | Reported Value Measurement [Member]
Assets:
Derivatives:	23,809	19,339
Liabilities:
Derivatives:	45,938	37,150
Interest rate swaps [Member] | Estimate of Fair Value Measurement [Member]
Assets:
Derivatives:	23,809	19,339
Liabilities:
Derivatives:	45,938	37,150
Interest Rate Forward Sales Commitments [Member] | Reported Value Measurement [Member]
Assets:
Derivatives:	338	142
Liabilities:
Derivatives:	25	118
Interest Rate Forward Sales Commitments [Member] | Estimate of Fair Value Measurement [Member]
Assets:
Derivatives:	338	142
Liabilities:
Derivatives:	25	118
Loan Participations and Assignments | Reported Value Measurement [Member]
Liabilities:
Derivatives:	19	67
Loan Participations and Assignments | Estimate of Fair Value Measurement [Member]
Liabilities:
Derivatives:	19	67
Fair Value, Inputs, Level 2 [Member] | Reported Value Measurement [Member]
Assets:
Securities—held-to-maturity	1,074,574	1,109,319
Fair Value, Inputs, Level 2 [Member] | Estimate of Fair Value Measurement [Member]
Assets:
Securities—held-to-maturity	846,061	933,513
Fair Value, Inputs, Level 3 [Member] | Reported Value Measurement [Member]
Assets:
Securities—held-to-maturity	7,582	8,648
Fair Value, Inputs, Level 3 [Member] | Estimate of Fair Value Measurement [Member]
Assets:
Securities—held-to-maturity	$ 7,592	$ 8,667