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	Jun. 30, 2013	Dec. 31, 2012		Jun. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 3,290,201	$ 3,235,714		$ 3,212,257
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,096,708	1,073,222
Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	137,027	137,504		130,319
Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	353,684	304,617
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	639,840	618,049		600,046
Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	233,967	230,031		211,705
One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	552,698	581,670		607,489
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	276,277	290,621
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,139,566	3,077,933	[1]
Pass (Risk Ratings 1-5) [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,047,077	1,016,964	[1]
Pass (Risk Ratings 1-5) [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	131,314	130,815	[1]
Pass (Risk Ratings 1-5) [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	329,004	274,407	[1]
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	607,626	581,846	[1]
Pass (Risk Ratings 1-5) [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	217,097	228,304	[1]
Pass (Risk Ratings 1-5) [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	535,884	560,781	[1]
Pass (Risk Ratings 1-5) [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	271,564	284,816	[1]
Pass (Risk Ratings 1-5) [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	81,000	77,000
Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	22,507	26,682
Special mention [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	12,631	14,332
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	481	3,146
Special mention [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	8,600	7,905
Special mention [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	653	713
Special mention [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0	438
Special mention [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	142	148
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	127,574	130,544
Substandard [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	36,456	41,382
Substandard [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	5,713	6,689
Substandard [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	24,199	27,064
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	23,604	28,287
Substandard [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	16,217	1,014
Substandard [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	16,814	20,451
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	4,571	5,657
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	554	555
Doubtful [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	544	544
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	10	11
Doubtful [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0	0
Doubtful [Member] | One- to four-family real estate [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	0	0
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, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0	0
Loss [Member] | One- to four-family real estate [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	3,264,100	3,201,324
Performing loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,091,898	1,066,643
Performing loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	136,692	137,504
Performing loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	350,909	300,945
Performing loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	637,017	613,299
Performing loans [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	233,967	230,031
Performing loans [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	539,336	565,829
Performing loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	274,281	287,073
Nonperforming loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	26,101	34,390	[2]
Nonperforming loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	4,810	6,579	[2]
Nonperforming loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	335	0	[2]
Nonperforming loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	2,775	3,672	[2]
Nonperforming loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	2,823	4,750	[2]
Nonperforming loans [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0	0	[2]
Nonperforming loans [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	13,362	15,841	[2]
Nonperforming loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 1,996	$ 3,548	[2]

[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, 2013 and December 31, 2012, in the commercial business category, $81 million and $77 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.