FAIR VALUE OF FINANCIAL INSTRUMENTS (Fair Value By Balance Sheet Location) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Assets:
Securities—trading	$ 23,466	$ 24,568
Securities—available-for-sale	1,339,057	800,917
Securities—held-to-maturity	268,663	270,528
Liabilities:
FHLB advances at fair value	263,349	54,216
Carrying Value
Assets:
Cash and cash equivalents	241,766	247,719
Securities—trading	23,466	24,568
Securities—available-for-sale	1,339,057	800,917
Securities—held-to-maturity	264,752	267,873
Loans receivable held for sale	71,905	246,353
Loans receivable	7,774,449	7,451,148
FHLB stock	20,854	12,506
Bank-owned life insurance	161,648	158,936
Mortgage servicing rights	14,754	15,249
Liabilities:
Demand, interest checking and money market accounts	5,860,984	5,552,690
Regular savings	1,577,292	1,523,391
Certificates of deposit	1,100,574	1,045,333
FHLB advances at fair value	263,349	54,216
Other borrowings	103,713	105,685
Junior subordinated debentures at fair value	97,280	95,200
Estimated Fair Value
Assets:
Cash and cash equivalents	241,766	247,719
Securities—trading	23,466	24,568
Securities—available-for-sale	1,339,057	800,917
Securities—held-to-maturity	268,663	270,528
Loans receivable held for sale	72,018	246,815
Loans receivable	7,666,707	7,337,608
FHLB stock	20,854	12,506
Bank-owned life insurance	161,648	158,936
Mortgage servicing rights	18,312	16,740
Liabilities:
Demand, interest checking and money market accounts	5,860,984	5,552,690
Regular savings	1,577,292	1,523,391
Certificates of deposit	1,082,829	1,028,866
FHLB advances at fair value	263,349	54,216
Other borrowings	103,713	105,685
Junior subordinated debentures at fair value	97,280	95,200
Interest rate swaps [Member] | Carrying Value
Assets:
Derivatives:	7,186	8,330
Liabilities:
Derivatives:	7,186	8,330
Interest rate swaps [Member] | Estimated Fair Value
Assets:
Derivatives:	7,186	8,330
Liabilities:
Derivatives:	7,186	8,330
Interest Rate Forward Sales Commitments [Member] | Carrying Value
Assets:
Derivatives:	664	482
Liabilities:
Derivatives:	115	289
Interest Rate Forward Sales Commitments [Member] | Estimated Fair Value
Assets:
Derivatives:	664	482
Liabilities:
Derivatives:	$ 115	$ 289