LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Type) (Details) (USD $)	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 3,213,523,000		$ 3,296,338,000	$ 3,225,246,000
Less allowance for loan losses	(78,783,000)	(80,221,000)	(82,912,000)	(86,128,000)	(92,000,000)	(97,401,000)
Total loans	3,134,740,000		3,213,426,000	3,139,118,000
Percent of total loans	100.00%		100.00%	100.00%
Unearned, unamortized loan fees (and costs)	9,000,000		10,000,000	10,000,000
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	477,871,000		469,806,000	474,863,000
Percent of total loans	14.90%		14.20%	14.70%
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	604,265,000		621,622,000	586,652,000
Percent of total loans	18.80%		18.90%	18.20%
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	138,716,000		139,710,000	134,146,000
Percent of total loans	4.30%		4.20%	4.20%
Commercial construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	28,598,000		42,391,000	38,124,000
Percent of total loans	0.90%		1.30%	1.20%
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	14,502,000		19,436,000	16,335,000
Percent of total loans	0.50%		0.60%	0.50%
One-to four-family construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	163,521,000		144,177,000	145,776,000
Percent of total loans	5.10%		4.40%	4.50%
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	79,932,000		97,491,000	96,875,000
Percent of total loans	2.50%		3.00%	3.00%
Land and land development - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	14,242,000		15,197,000	19,173,000
Percent of total loans	0.40%		0.50%	0.60%
Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	603,606,000		601,440,000	580,876,000
Percent of total loans	18.80%		18.20%	18.00%
Agricultural business, including secured by farming [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	219,084,000		218,171,000	211,571,000
Percent of total loans	6.80%		6.60%	6.60%
One- to four-family real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	594,413,000		642,501,000	639,909,000
Percent of total loans	18.50%		19.50%	19.80%
Total consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	274,773,000		284,396,000	280,946,000
Percent of total loans	8.50%		8.60%	8.70%
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	103,393,000		103,347,000	98,794,000
Percent of total loans	3.20%		3.10%	3.10%
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 171,380,000		$ 181,049,000	$ 182,152,000
Percent of total loans	5.30%		5.50%	5.60%