FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value By Balance Sheet Location) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Assets:
Securities—trading	$ 21,040	$ 25,636
Securities—available-for-sale	1,608,224	1,551,557
Securities—held-to-maturity	449,237	237,805
Liabilities:
FHLB advances at fair value	247,000	450,000
Carrying Value
Assets:
Cash and cash equivalents	295,001	307,735
Securities—trading	21,040	25,636
Securities—available-for-sale	1,608,224	1,551,557
Loans receivable held for sale	182,428	210,447
Loans receivable	9,285,744	9,305,357
FHLB stock	20,247	28,342
Bank-owned life insurance	193,140	192,088
Mortgage servicing rights	14,277	14,148
Liabilities:
Demand, interest checking and money market accounts	7,285,966	6,994,197
Regular savings	1,997,265	1,934,041
Certificates of deposit	1,166,306	1,120,403
FHLB advances at fair value	247,000	450,000
Other borrowings	128,764	118,474
Junior subordinated debentures at fair value	99,795	119,304
Estimated Fair Value
Assets:
Cash and cash equivalents	295,001	307,735
Securities—trading	21,040	25,636
Securities—available-for-sale	1,608,224	1,551,557
Loans receivable held for sale	182,766	210,670
Loans receivable	9,272,174	9,304,340
FHLB stock	20,247	28,342
Bank-owned life insurance	193,140	192,088
Mortgage servicing rights	20,931	22,611
Liabilities:
Demand, interest checking and money market accounts	7,285,966	6,994,197
Regular savings	1,997,265	1,934,041
Certificates of deposit	1,173,126	1,117,921
FHLB advances at fair value	251,978	452,720
Other borrowings	128,764	118,474
Junior subordinated debentures at fair value	99,795	119,304
Interest rate swaps [Member] | Carrying Value
Assets:
Derivatives:	42,687	15,202
Liabilities:
Derivatives:	23,280	10,966
Interest rate swaps [Member] | Estimated Fair Value
Assets:
Derivatives:	42,687	15,202
Liabilities:
Derivatives:	23,280	10,966
Interest Rate Forward Sales Commitments [Member] | Carrying Value
Assets:
Derivatives:	3,325	1,108
Liabilities:
Derivatives:	4,448	674
Interest Rate Forward Sales Commitments [Member] | Estimated Fair Value
Assets:
Derivatives:	3,325	1,108
Liabilities:
Derivatives:	4,448	674
Fair Value, Inputs, Level 2 [Member] | Carrying Value
Assets:
Securities—held-to-maturity	435,119	233,241
Fair Value, Inputs, Level 2 [Member] | Estimated Fair Value
Assets:
Securities—held-to-maturity	446,412	234,952
Fair Value, Inputs, Level 3 [Member] | Carrying Value
Assets:
Securities—held-to-maturity	2,825	2,853
Fair Value, Inputs, Level 3 [Member] | Estimated Fair Value
Assets:
Securities—held-to-maturity	$ 2,825	$ 2,853