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	Mar. 31, 2013	Dec. 31, 2012		Mar. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 3,240,321	$ 3,235,714		$ 3,229,662
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,100,203	1,073,222
Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	134,290	137,504		132,306
Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	331,708	304,617
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	619,478	618,049		609,497
Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	210,225	230,031		188,955
One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	566,730	581,670		619,511
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	277,687	290,621
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,101,049	3,077,933	[1]
Pass (Risk Ratings 1-5) [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,049,911	1,016,964	[1]
Pass (Risk Ratings 1-5) [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	127,315	130,815	[1]
Pass (Risk Ratings 1-5) [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	304,986	274,407	[1]
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	590,905	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	209,291	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	546,874	560,781	[1]
Pass (Risk Ratings 1-5) [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	271,767	284,816	[1]
Pass (Risk Ratings 1-5) [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	78,000	77,000
Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	21,418	26,682
Special mention [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	13,338	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	2,015	3,146
Special mention [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	4,798	7,905
Special mention [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	685	713
Special mention [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	437	438
Special mention [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	145	148
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	117,299	130,544
Substandard [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	36,410	41,382
Substandard [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	6,975	6,689
Substandard [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	24,707	27,064
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	23,764	28,287
Substandard [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	249	1,014
Substandard [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	19,419	20,451
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	5,775	5,657
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	555	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	11	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	3,206,915	3,201,324
Performing loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,093,477	1,066,643
Performing loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	133,951	137,504
Performing loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	327,979	300,945
Performing loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	615,108	613,299
Performing loans [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	210,225	230,031
Performing loans [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	551,611	565,829
Performing loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	274,564	287,073
Nonperforming loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	33,406	34,390	[2]
Nonperforming loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	6,726	6,579	[2]
Nonperforming loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	339	0	[2]
Nonperforming loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,729	3,672	[2]
Nonperforming loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	4,370	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	15,119	15,841	[2]
Nonperforming loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 3,123	$ 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 March 31, 2013 and December 31, 2012, in the commercial business category, $78 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.