LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Risk-Rate and Non-Risk Rated Loans by Grade and Other Characteristic) (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		$ 7,451,148	$ 7,314,504
Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		1,352,999	1,327,807
Investment Properties Commerical Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		1,986,336	1,765,353
Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		248,150	472,976
Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		124,068	72,103
Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		124,126	63,846
One-to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		375,704	278,469
Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		170,004	126,773
Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		29,184	33,179
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		1,207,879	1,207,944
Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		369,156	376,531
One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		813,077	952,633
Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		493,211	478,420
Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		157,254	158,470
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	7,282,408	7,148,698
Pass (Risk Ratings 1-5) [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		225,000	150,000
Pass (Risk Ratings 1-5) [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	1,313,142	1,281,561
Pass (Risk Ratings 1-5) [Member] | Investment Properties Commerical Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	1,948,822	1,740,720
Pass (Risk Ratings 1-5) [Member] | Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	247,258	468,467
Pass (Risk Ratings 1-5) [Member] | Commercial Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	124,068	72,103
Pass (Risk Ratings 1-5) [Member] | Multifamily construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	124,126	63,846
Pass (Risk Ratings 1-5) [Member] | One-to four-family construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	371,636	275,154
Pass (Risk Ratings 1-5) [Member] | Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	167,764	121,536
Pass (Risk Ratings 1-5) [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	25,090	25,786
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	1,148,585	1,167,933
Pass (Risk Ratings 1-5) [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	356,656	354,760
Pass (Risk Ratings 1-5) [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	807,837	943,098
Pass (Risk Ratings 1-5) [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	490,877	476,448
Pass (Risk Ratings 1-5) [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable	[1]	156,547	157,286
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		77,691	77,632
Special Mention [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		14,394	19,400
Special Mention [Member] | Investment Properties Commerical Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		23,846	11,528
Special Mention [Member] | Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	138
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] | Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	76
Special Mention [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	2,310
Special Mention [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		35,036	25,286
Special Mention [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		3,335	17,526
Special Mention [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		967	1,346
Special Mention [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		5	0
Special Mention [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		108	22
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		91,042	88,164
Substandard [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		25,463	26,846
Substandard [Member] | Investment Properties Commerical Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		13,668	13,105
Substandard [Member] | Multifamily Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		892	4,371
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		4,068	3,315
Substandard [Member] | Residential Land and Land Development [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		2,240	5,161
Substandard [Member] | Land and land development - commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		4,094	5,083
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		24,258	14,725
Substandard [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		9,165	4,245
Substandard [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		4,273	8,189
Substandard [Member] | Consumer secured by one- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		2,327	1,967
Substandard [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		594	1,157
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		7	10
Doubtful [Member] | Owner-occupied Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | Investment Properties Commerical Real Estate [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] | Residential Land and Land Development [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 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Doubtful [Member] | One- to four-family residential [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		2	5
Doubtful [Member] | Consumer Borrower [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		5	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] | Investment Properties Commerical Real Estate [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] | Residential Land and Land Development [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 [Member]
Financing Receivable, Recorded Investment [Line Items]
Loans receivable		0	0
Loss [Member] | One- to four-family residential [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

[1] (1) The Pass category includes some performing loans that are part of homogenous pools which are not individually risk-rated. This includes all consumer loans, all one- to four-family residential loans and, as of December 31, 2016 and 2015, in the commercial business category, $225.0 million and $150.0 million, respectively, of credit-scored small business loans. As loans in these homogeneous pools become non-accrual, they are individually risk-rated.