LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Type) (Details) (USD $)	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 3,275,436,000		$ 3,235,714,000	$ 3,213,523,000
Less allowance for loan losses	(76,657,000)	(76,853,000)	(77,491,000)	(78,783,000)	(80,221,000)	(82,912,000)
Total loans	3,198,779,000		3,158,223,000	3,134,740,000
Percent of total loans	100.00%		100.00%	100.00%
Unearned, unamortized loan fees (and costs)	8,800,000		8,900,000	9,000,000
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	508,341,000		489,581,000	477,871,000
Percent of total loans	15.50%		15.10%	14.90%
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	613,757,000		583,641,000	604,265,000
Percent of total loans	18.80%		18.00%	18.80%
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	133,770,000		137,504,000	138,716,000
Percent of total loans	4.10%		4.30%	4.30%
Commercial construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	18,730,000		30,229,000	28,598,000
Percent of total loans	0.60%		0.90%	0.90%
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	33,888,000		22,581,000	14,502,000
Percent of total loans	1.00%		0.70%	0.50%
One-to four-family construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	194,187,000		160,815,000	163,521,000
Percent of total loans	5.90%		5.00%	5.10%
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	75,576,000		77,010,000	79,932,000
Percent of total loans	2.30%		2.40%	2.50%
Land and land development - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	11,231,000		13,982,000	14,242,000
Percent of total loans	0.30%		0.40%	0.40%
Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	635,658,000		618,049,000	603,606,000
Less allowance for loan losses	(10,676,000)	(10,806,000)	(9,957,000)	(10,701,000)	(12,352,000)	(15,159,000)
Percent of total loans	19.40%		19.10%	18.80%
Agricultural business, including secured by farming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	223,187,000		230,031,000	219,084,000
Less allowance for loan losses	(3,411,000)	(3,805,000)	(2,295,000)	(2,342,000)	(1,294,000)	(1,548,000)
Percent of total loans	6.80%		7.10%	6.80%
One- to four-family real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	543,263,000		581,670,000	594,413,000
Percent of total loans	16.60%		18.00%	18.50%
Total consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	283,848,000		290,621,000	274,773,000
Less allowance for loan losses	(948,000)	(1,011,000)	(1,348,000)	(1,321,000)	(1,365,000)	(1,253,000)
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	113,829,000		120,498,000	103,393,000
Percent of total loans	3.50%		3.70%	3.20%
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 170,019,000		$ 170,123,000	$ 171,380,000
Percent of total loans	5.20%		5.30%	5.30%