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, 2012		Dec. 31, 2011		Sep. 30, 2011
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 3,213,523		$ 3,296,338		$ 3,225,246
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,082,136		1,091,428
Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	138,716		139,710		134,146
Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	300,795		318,692
Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	603,606		601,440		580,876
Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	219,084		218,171		211,571
One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	594,413		642,501		639,909
Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	274,773		284,396		280,946
Pass (Risk Ratings 1-5) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,030,628	[1]	3,034,355	[1]
Pass (Risk Ratings 1-5) [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,018,552	[1]	1,003,990	[1]
Pass (Risk Ratings 1-5) [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	131,782	[1]	132,108	[1]
Pass (Risk Ratings 1-5) [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	263,281	[1]	257,685	[1]
Pass (Risk Ratings 1-5) [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	560,320	[1]	542,625	[1]
Pass (Risk Ratings 1-5) [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	217,084	[1]	213,512	[1]
Pass (Risk Ratings 1-5) [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	571,146	[1]	607,793	[1]
Pass (Risk Ratings 1-5) [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	268,463	[1]	276,642	[1]
Pass (Risk Ratings 1-5) [Member] | Small Credit-Scored Business Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	70,000		58,000
Special mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	36,894		53,654
Special mention [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	19,223		29,751
Special mention [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0		5,000
Special mention [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	3,267		3,359
Special mention [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	13,482		13,447
Special mention [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	331		923
Special mention [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	440		772
Special mention [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	151		402
Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	145,943		207,993
Substandard [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	44,361		57,687
Substandard [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	6,934		2,602
Substandard [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	34,189		57,648
Substandard [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	29,804		45,032
Substandard [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,669		3,736
Substandard [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	22,827		33,936
Substandard [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	6,159		7,352
Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	58		336
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	58		0
Doubtful [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0		336
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	3,174,812		3,221,026
Performing loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	1,076,562		1,082,202
Performing loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	138,716		139,348
Performing loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	293,345		290,961
Performing loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	597,433		587,976
Performing loans [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	218,438		216,275
Performing loans [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	578,142		622,946
Performing loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	272,176		281,318
Nonperforming loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	38,711		75,312	[2]
Nonperforming loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	5,574		9,226	[2]
Nonperforming loans [Member] | Multifamily real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	0		362	[2]
Nonperforming loans [Member] | Construction and Land [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	7,450		27,731	[2]
Nonperforming loans [Member] | Commercial business [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	6,173		13,464	[2]
Nonperforming loans [Member] | Agricultural business, including secured by farming [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	646		1,896	[2]
Nonperforming loans [Member] | One- to four-family real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	16,271		19,555	[2]
Nonperforming loans [Member] | Consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans outstanding	$ 2,597		$ 3,078	[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, 2012 and December 31, 2011, in the commercial business category, $70 million and $58 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.