LOANS RECEIVABLE AND THE ALLOWANCE FOR LOAN LOSSES (Loans by Type) (Details) (USD $)	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	$ 4,114,818,000	$ 3,833,820,000	$ 3,522,912,000
Less allowance for loan losses	(75,365,000)	(75,907,000)	(74,371,000)	(74,258,000)
Total loans, net	4,039,453,000us-gaap_LoansReceivableNet	3,757,913,000us-gaap_LoansReceivableNet
Loans and Leases Receivable, Allowance	75,365,000	75,907,000
Loans and Leases Receivable, Gross	4,114,818,000	3,833,820,000
Concentration Risk, Percentage	100.00%us-gaap_ConcentrationRiskPercentage1	100.00%us-gaap_ConcentrationRiskPercentage1
Unearned loan (fees) in excess of unamortized costs	10,600,000	5,800,000
Discount on acquired loans	5,000,000	148,000
Commerical real estate - owner-occupied [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	627,531,000	546,783,000
Loans and Leases Receivable, Gross	627,531,000	546,783,000
Concentration Risk, Percentage	15.30%	14.30%
Commerical real estate - investment properties [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	936,693,000	856,942,000
Loans and Leases Receivable, Gross	936,693,000	856,942,000
Concentration Risk, Percentage	22.80%	22.30%
Multifamily real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	208,687,000	167,524,000	153,003,000
Less allowance for loan losses	(4,401,000)	(4,562,000)	(5,652,000)	(5,306,000)
Loans and Leases Receivable, Gross	208,687,000	167,524,000
Concentration Risk, Percentage	5.10%	4.40%
Commercial construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	30,434,000	17,337,000
Loans and Leases Receivable, Gross	30,434,000	17,337,000
Concentration Risk, Percentage	0.70%	0.40%
Multifamily construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	56,201,000	60,193,000
Loans and Leases Receivable, Gross	56,201,000	60,193,000
Concentration Risk, Percentage	1.40%	1.60%
One-to four-family construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	228,224,000	219,889,000
Loans and Leases Receivable, Gross	228,224,000	219,889,000
Concentration Risk, Percentage	5.50%	5.70%
Land and land development - residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	98,930,000	102,435,000
Loans and Leases Receivable, Gross	98,930,000	102,435,000
Concentration Risk, Percentage	2.40%	2.70%
Land and land development - commercial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	17,174,000	11,152,000
Loans and Leases Receivable, Gross	17,174,000	11,152,000
Concentration Risk, Percentage	0.40%	0.30%
Commercial business [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	776,579,000	723,964,000	716,546,000
Less allowance for loan losses	(12,892,000)	(12,043,000)	(11,363,000)	(11,773,000)
Loans and Leases Receivable, Gross	776,579,000	723,964,000
Concentration Risk, Percentage	18.90%	18.90%
Agricultural business, including secured by farmland [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	208,635,000	238,499,000	208,817,000
Less allowance for loan losses	(3,732,000)	(2,821,000)	(2,636,000)	(2,841,000)
Loans and Leases Receivable, Gross	208,635,000	238,499,000
Concentration Risk, Percentage	5.10%	6.20%
One- to four-family residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	552,423,000	539,894,000	517,621,000
Less allowance for loan losses	(8,141,000)	(8,447,000)	(10,913,000)	(11,486,000)
Loans and Leases Receivable, Gross	552,423,000	539,894,000
Concentration Risk, Percentage	13.40%	14.10%
Consumer secured by one- to four-family [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	233,643,000	222,205,000
Loans and Leases Receivable, Gross	233,643,000	222,205,000
Concentration Risk, Percentage	5.70%	5.80%
Consumer - other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans outstanding	139,664,000	127,003,000
Loans and Leases Receivable, Gross	$ 139,664,000	$ 127,003,000
Concentration Risk, Percentage	3.30%	3.30%

Loans Receivable, Including Loans Held-for-sale, Gross

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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A valuation allowance for financing receivables that are expected to be uncollectible.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

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Disclosure of the unamortized amount of the discount on the note or receivable which is deducted from the face amount of the receivable or loan. The discount or premium is the difference between the present value and the face amount.

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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