LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Risk-Rate and Non-Risk Rated Loans by Grade and Other Characteristic) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 3,418,445		$ 3,235,714
Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,195,058		1,073,222
Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	137,153		137,504
Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	351,258		304,617
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	682,169		618,049
Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	228,291		230,031
One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	529,494		581,670
Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	295,022		290,621
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,308,889	[1]	3,077,933	[2]
Pass (Risk Ratings 1-5) [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,160,921	[1]	1,016,964	[2]
Pass (Risk Ratings 1-5) [Member] | Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	131,523	[1]	130,815	[2]
Pass (Risk Ratings 1-5) [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	332,150	[1]	274,407	[2]
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	655,007	[1]	581,846	[2]
Pass (Risk Ratings 1-5) [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	94,000		77,000
Pass (Risk Ratings 1-5) [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	225,329	[1]	228,304	[2]
Pass (Risk Ratings 1-5) [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	511,967	[1]	560,781	[2]
Pass (Risk Ratings 1-5) [Member] | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	291,992	[1]	284,816	[2]
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	18,115		26,682
Special Mention [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	6,614		14,332
Special Mention [Member] | Multifamily [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	350		3,146
Special Mention [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	10,484		7,905
Special Mention [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	561		713
Special Mention [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0		438
Special Mention [Member] | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	106		148
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	90,888		130,544
Substandard [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	26,979		41,382
Substandard [Member] | Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	5,630		6,689
Substandard [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	18,758		27,064
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	16,669		28,287
Substandard [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	2,401		1,014
Substandard [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	17,527		20,451
Substandard [Member] | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	2,924		5,657
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	553		555
Doubtful [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	544		544
Doubtful [Member] | Multifamily [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	9		11
Doubtful [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0		0
Doubtful [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0		0
Doubtful [Member] | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0		0
Performing loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,393,677		3,201,324
Performing loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,188,771		1,066,643
Performing loans [Member] | Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	137,153		137,504
Performing loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	350,065		300,945
Performing loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	681,445		613,299
Performing loans [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	228,187		230,031
Performing loans [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	514,351		565,829
Performing loans [Member] | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	293,705		287,073
Nonperforming loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	24,768	[3]	34,390	[3]
Nonperforming loans [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	6,287	[3]	6,579	[3]
Nonperforming loans [Member] | Multifamily [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0	[3]	0	[3]
Nonperforming loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,193	[3]	3,672	[3]
Nonperforming loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	724	[3]	4,750	[3]
Nonperforming loans [Member] | Agricultural Business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	104	[3]	0	[3]
Nonperforming loans [Member] | One- to four-family residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	15,143	[3]	15,841	[3]
Nonperforming loans [Member] | Consumer
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 1,317	[3]	$ 3,548	[3]

[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, 2013, in the commercial business category, $94 million of credit-scored small business loans. As loans in these pools become non-performing, they are individually risk-rated.

[2] 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, 2012, in the commercial business category, $77 million of credit-scored small business loans. As loans in these pools become non-performing, they are individually risk-rated.

[3] Non-performing loans include loans on non-accrual status and loans more than 90 days delinquent, but still accruing interest.