LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Risk-Rated and Non-Risk Rated Loans by Grade and Other Characteristic) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	$ 7,421,255	$ 7,451,148	$ 7,185,999
Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	1,361,095	1,352,999
Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	2,011,618	1,986,336
Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	254,246	248,150	307,019
Commercial construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	141,505	124,068
Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	114,728	124,126
One- to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	366,191	375,704
Land and land development - residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	151,649	170,004
Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	29,597	29,184
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	1,224,541	1,207,879	1,224,915
Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	313,374	369,156	340,350
One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	802,991	813,077	$ 910,719
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	493,495	493,211
Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	156,225	157,254
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	7,250,587	7,282,408
Pass (Risk Ratings 1-5) [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	1,323,022	1,313,142
Pass (Risk Ratings 1-5) [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	1,985,876	1,948,822
Pass (Risk Ratings 1-5) [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	253,100	247,258
Pass (Risk Ratings 1-5) [Member] | Commercial construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	141,505	124,068
Pass (Risk Ratings 1-5) [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	114,728	124,126
Pass (Risk Ratings 1-5) [Member] | One- to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	362,563	371,636
Pass (Risk Ratings 1-5) [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	149,048	167,764
Pass (Risk Ratings 1-5) [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	25,682	25,090
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	1,154,776	1,148,585
Pass (Risk Ratings 1-5) [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	242,300	225,000
Pass (Risk Ratings 1-5) [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	296,883	356,656
Pass (Risk Ratings 1-5) [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	796,664	807,837
Pass (Risk Ratings 1-5) [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	490,977	490,877
Pass (Risk Ratings 1-5) [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	155,763	156,547
Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	41,536	77,691
Special mention [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	5,424	14,394
Special mention [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	10,649	23,846
Special mention [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Special mention [Member] | Commercial construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Special mention [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Special mention [Member] | One- to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Special mention [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Special mention [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Special mention [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	15,937	35,036
Special mention [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	8,501	3,335
Special mention [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	942	967
Special mention [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	3	5
Special mention [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	80	108
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	129,132	91,042
Substandard [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	32,649	25,463
Substandard [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	15,093	13,668
Substandard [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	1,146	892
Substandard [Member] | Commercial construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Substandard [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Substandard [Member] | One- to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	3,628	4,068
Substandard [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	2,601	2,240
Substandard [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	3,915	4,094
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	53,828	24,258
Substandard [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	7,990	9,165
Substandard [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	5,385	4,273
Substandard [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	2,515	2,327
Substandard [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	382	594
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	7
Doubtful [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Commercial construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | One- to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Doubtful [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	2
Doubtful [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	5
Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Commercial real estate - investment properties [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Commercial construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | One- to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Land and land development - residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	0	0
Loss [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	$ 0	$ 0