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	Sep. 30, 2013	Dec. 31, 2012		Sep. 30, 2012
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 3,275,436	$ 3,235,714		$ 3,213,523
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,122,098	1,073,222		1,082,136
Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	133,770	137,504		138,716
Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	333,612	304,617		300,795
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	635,658	618,049		603,606
Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	223,187	230,031		219,084
One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	543,263	581,670		594,413
Total consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	283,848	290,621		274,773
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,155,251	3,077,933	[1]
Pass (Risk Ratings 1-5) [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,084,540	1,016,964	[1]
Pass (Risk Ratings 1-5) [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	126,360	130,815	[1]
Pass (Risk Ratings 1-5) [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	313,108	274,407	[1]
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	611,668	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	212,012	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	527,655	560,781	[1]
Pass (Risk Ratings 1-5) [Member] | Total consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	279,908	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	13,076	26,682
Special mention [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	6,033	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	5,802	7,905
Special mention [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	621	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] | Total consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	139	148
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	106,556	130,544
Substandard [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	30,981	41,382
Substandard [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	7,410	6,689
Substandard [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	20,023	27,064
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	18,179	28,287
Substandard [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	10,554	1,014
Substandard [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	15,608	20,451
Substandard [Member] | Total consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,801	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 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	9	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] | Total 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] | Total 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	3,250,574	3,201,324
Performing loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,117,336	1,066,643
Performing loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	131,736	137,504
Performing loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	331,710	300,945
Performing loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	634,671	613,299
Performing loans [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	223,187	230,031
Performing loans [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	529,772	565,829
Performing loans [Member] | Total consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	282,162	287,073
Nonperforming loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	24,862	34,390	[2]
Nonperforming loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	4,762	6,579	[2]
Nonperforming loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	2,034	0	[2]
Nonperforming loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,902	3,672	[2]
Nonperforming loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	987	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	13,491	15,841	[2]
Nonperforming loans [Member] | Total consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 1,686	$ 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 September 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.