FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value By Balance Sheet Location) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Securities—trading	$ 26,875	$ 24,980
Debt Securities, Available-for-sale	3,446,575	2,322,593
Securities—held-to-maturity	466,002	448,681
Securities purchased under agreements to resell	300,000	0
Liabilities:
FHLB advances at fair value	50,000	150,000
Subordinated notes, net	98,472	98,201
Carrying Value
Assets:
Cash and cash equivalents	2,200,582	1,234,183
Securities—trading	26,875	24,980
Debt Securities, Available-for-sale	3,446,575	2,322,593
Securities purchased under agreements to resell	300,000	0
Loans receivable held for sale	63,678	243,795
Loans receivable	9,218,384	9,870,982
FHLB stock	12,000	16,358
Bank-owned life insurance	192,950	191,830
Mortgage servicing rights	15,753	15,223
Liabilities:
Demand, interest checking and money market accounts	10,539,628	9,253,494
Regular savings	2,773,995	2,398,482
Certificates of deposit	851,054	915,320
FHLB advances at fair value	50,000	150,000
Other borrowings	247,358	184,785
Subordinated notes, net		98,201
Junior subordinated debentures at fair value	124,853	116,974
Estimated Fair Value
Assets:
Cash and cash equivalents	2,200,582	1,234,183
Securities—trading	26,875	24,980
Debt Securities, Available-for-sale	3,446,575	2,322,593
Securities purchased under agreements to resell	300,000	0
Loans receivable held for sale	64,245	245,667
Loans receivable	9,271,840	9,810,293
FHLB stock	12,000	16,358
Bank-owned life insurance	192,950	191,830
Mortgage servicing rights	22,814	18,084
Liabilities:
Demand, interest checking and money market accounts	10,539,628	9,253,494
Regular savings	2,773,995	2,398,482
Certificates of deposit	851,780	919,920
FHLB advances at fair value	50,629	152,779
Other borrowings	247,358	184,785
Subordinated notes, net	105,875	98,201
Junior subordinated debentures at fair value	124,853	116,974
Interest rate swaps [Member] | Carrying Value
Assets:
Derivatives:	25,627	39,066
Liabilities:
Derivatives:	15,550	22,336
Interest rate swaps [Member] | Estimated Fair Value
Assets:
Derivatives:	25,627	39,066
Liabilities:
Derivatives:	15,550	22,336
Interest Rate Forward Sales Commitments [Member] | Carrying Value
Assets:
Derivatives:	2,309	5,641
Liabilities:
Derivatives:	136	1,755
Interest Rate Forward Sales Commitments [Member] | Estimated Fair Value
Assets:
Derivatives:	2,309	5,641
Liabilities:
Derivatives:	136	1,755
Fair Value, Inputs, Level 2 [Member] | Carrying Value
Assets:
Securities—held-to-maturity	445,499	410,038
Fair Value, Inputs, Level 2 [Member] | Estimated Fair Value
Assets:
Securities—held-to-maturity	463,913	436,882
Fair Value, Inputs, Level 3 [Member] | Carrying Value
Assets:
Securities—held-to-maturity	2,313	11,769
Fair Value, Inputs, Level 3 [Member] | Estimated Fair Value
Assets:
Securities—held-to-maturity	$ 2,089	$ 11,799