LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Type) (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 3,833,820,000	$ 3,418,445,000
Less allowance for loan losses	(75,907,000)	(74,258,000)	(76,759,000)
Total loans, net	3,757,913,000	3,344,187,000
Percent of total loans	100.00%	100.00%
Unearned, unamortized loan fees (and costs)	(5,800,000)	(8,300,000)
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	546,783,000	502,601,000
Percent of total loans	14.30%	14.70%
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	856,942,000	692,457,000
Percent of total loans	22.30%	20.20%
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	167,524,000	137,153,000
Less allowance for loan losses	(4,562,000)	(5,306,000)	(4,506,000)
Percent of total loans	4.40%	4.00%
Commercial construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	17,337,000	12,168,000
Percent of total loans	0.40%	0.40%
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	60,193,000	52,081,000
Percent of total loans	1.60%	1.50%
One-to four-family construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	219,889,000	200,864,000
Percent of total loans	5.70%	5.90%
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	102,435,000	75,695,000
Percent of total loans	2.70%	2.20%
Land and land development - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	11,152,000	10,450,000
Percent of total loans	0.30%	0.30%
Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	723,964,000	682,169,000
Less allowance for loan losses	(12,043,000)	(11,773,000)	(9,957,000)
Percent of total loans	18.90%	20.00%
Agricultural business, including secured by farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	238,499,000	228,291,000
Less allowance for loan losses	(3,821,000)	(2,841,000)	(2,295,000)
Percent of total loans	6.20%	6.70%
One- to four-family residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	539,894,000	529,494,000
Less allowance for loan losses	(5,447,000)	(11,486,000)	(16,475,000)
Percent of total loans	14.10%	15.50%
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	222,205,000	173,188,000
Percent of total loans	5.80%	5.10%
Consumer - other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 127,003,000	$ 121,834,000
Percent of total loans	3.30%	3.50%