FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value By Balance Sheet Location) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Securities—trading	$ 23,276	$ 25,636
Securities—available-for-sale	1,758,384	1,551,557
Securities—held-to-maturity	450,806	237,805
Equity securities	450,255	0
Liabilities:
FHLB advances at fair value	150,000	450,000
Subordinated notes, net	98,114	0
Carrying Value
Assets:
Cash and cash equivalents	705,538	307,735
Securities—trading	23,276	25,636
Securities—available-for-sale	1,758,384	1,551,557
Loans receivable held for sale	185,938	210,447
Loans receivable	10,163,917	9,305,357
FHLB stock	16,363	28,342
Bank-owned life insurance	191,755	192,088
Mortgage servicing rights	14,815	14,148
Equity securities		0
Liabilities:
Demand, interest checking and money market accounts	8,967,702	6,994,197
Regular savings	2,332,287	1,934,041
Certificates of deposit	915,352	1,120,403
FHLB advances at fair value	150,000	450,000
Other borrowings	176,983	118,474
Subordinated notes, net		0
Junior subordinated debentures at fair value	109,821	119,304
Estimated Fair Value
Assets:
Cash and cash equivalents	705,538	307,735
Securities—trading	23,276	25,636
Securities—available-for-sale	1,758,384	1,551,557
Loans receivable held for sale	186,544	210,670
Loans receivable	10,091,600	9,304,340
FHLB stock	16,363	28,342
Bank-owned life insurance	191,755	192,088
Mortgage servicing rights	17,954	22,611
Equity securities	450,255	0
Liabilities:
Demand, interest checking and money market accounts	8,967,702	6,994,197
Regular savings	2,332,287	1,934,041
Certificates of deposit	921,332	1,117,921
FHLB advances at fair value	153,661	452,720
Other borrowings	176,983	118,474
Subordinated notes, net	98,114	0
Junior subordinated debentures at fair value	109,821	119,304
Interest rate swaps [Member] | Carrying Value
Assets:
Derivatives:	43,506	15,202
Liabilities:
Derivatives:	23,927	10,966
Interest rate swaps [Member] | Estimated Fair Value
Assets:
Derivatives:	43,506	15,202
Liabilities:
Derivatives:	23,927	10,966
Interest Rate Forward Sales Commitments [Member] | Carrying Value
Assets:
Derivatives:	10,473	1,108
Liabilities:
Derivatives:	1,510	674
Interest Rate Forward Sales Commitments [Member] | Estimated Fair Value
Assets:
Derivatives:	10,473	1,108
Liabilities:
Derivatives:	1,510	674
Fair Value, Inputs, Level 2 [Member] | Carrying Value
Assets:
Securities—held-to-maturity	426,380	233,241
Fair Value, Inputs, Level 2 [Member] | Estimated Fair Value
Assets:
Securities—held-to-maturity	448,051	234,952
Fair Value, Inputs, Level 3 [Member] | Carrying Value
Assets:
Securities—held-to-maturity	2,755	2,853
Fair Value, Inputs, Level 3 [Member] | Estimated Fair Value
Assets:
Securities—held-to-maturity	$ 2,755	$ 2,853