LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Risk-Rated and Non-Risk Rated Loans by Grade and Other Characteristic) (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		$ 4,246,476	$ 3,833,820
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		1,613,038	1,403,725
Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		205,276	167,524
Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		457,331	411,006
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		811,623	723,964
Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		230,964	238,499
One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		542,961	539,894
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		385,283	349,208
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[1]	4,154,070	3,737,037
Pass (Risk Ratings 1-5) [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[1]	1,585,198	1,375,885
Pass (Risk Ratings 1-5) [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[1]	203,580	166,712
Pass (Risk Ratings 1-5) [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[1]	440,657	395,356
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[1]	789,478	691,143
Pass (Risk Ratings 1-5) [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		138,000	115,000
Pass (Risk Ratings 1-5) [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[1]	219,667	234,101
Pass (Risk Ratings 1-5) [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[1]	533,293	527,384
Pass (Risk Ratings 1-5) [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[1]	382,197	346,456
Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		29,760	32,428
Special mention [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		6,122	3,717
Special mention [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Special mention [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Special mention [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		15,468	27,453
Special mention [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		7,935	1,055
Special mention [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		150	63
Special mention [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		85	140
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		62,634	64,344
Substandard [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		21,718	24,123
Substandard [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		1,696	812
Substandard [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		16,674	15,650
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		6,677	5,368
Substandard [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		3,362	3,343
Substandard [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		9,518	12,447
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		2,989	2,601
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		12	11
Doubtful [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Doubtful [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Doubtful [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Doubtful [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Doubtful [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Doubtful [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Doubtful [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		12	11
Loss [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Loss [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Loss [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Loss [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Loss [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Loss [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Loss [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Loss [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		0	0
Performing loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		4,223,185	3,817,083
Performing loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		1,610,132	1,402,328
Performing loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		204,706	167,524
Performing loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		448,226	409,731
Performing loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		811,444	723,427
Performing loans [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		229,404	236,902
Performing loans [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		535,323	529,292
Performing loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding		383,950	347,879
Nonperforming loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[2]	23,291	16,737
Nonperforming loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[2]	2,906	1,397
Nonperforming loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[2]	570	0
Nonperforming loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[2]	9,105	1,275
Nonperforming loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[2]	179	537
Nonperforming loans [Member] | Agricultural Business/Farmland [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[2]	1,560	1,597
Nonperforming loans [Member] | One- to four-family [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[2]	7,638	10,602
Nonperforming loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	[2]	$ 1,333	$ 1,329

[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 June 30, 2015 and December 31, 2014, in the commercial business category, $138 million and $115 million, respectively, of credit-scored small business loans. As loans in these pools become non-performing, they are individually risk-rated.

[2] Non-performing loans include non-accrual loans and loans past due greater than 90 days and on accrual status.