FAIR VALUE DISCLOSURES (Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Investment securities:
Available for sale	$ 1,329,957	$ 1,445,689
Held to maturity debt securities, fair value	595,815	614,272
FRB and FHLB stock	30,707	30,458
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Assets:
Cash and cash equivalents	162,058	205,402
Investment securities:
Available for sale	1,329,957	1,445,689
Held to maturity debt securities, fair value	595,815	614,272
Loans held for portfolio	3,350,710	2,937,948
Loans held for sale	39,041	31,411
Derivative instruments	528	286
Accrued interest receivable	16,764	15,064
Financial Liabilities:
Deposits	4,897,473	4,848,582
Securities sold under agreements to repurchase	31,672	64,875
Accrued interest payable	808	831
Subordinated debentures	272,928	303,191
Liability for Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	12	12
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash and cash equivalents	162,058	205,402
Investment securities:
Available for sale	1,976	1,967
Held to maturity debt securities, fair value	0	0
Loans held for portfolio	0	0
Loans held for sale	0	0
Derivative instruments	0	0
Accrued interest receivable	16,764	15,064
Financial Liabilities:
Deposits	4,117,938	3,923,627
Securities sold under agreements to repurchase	31,672	64,875
Accrued interest payable	808	831
Subordinated debentures	0	0
Liability for Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 2 [Member]
Financial Assets:
Cash and cash equivalents	0	0
Investment securities:
Available for sale	1,327,981	1,443,722
Held to maturity debt securities, fair value	595,815	614,272
Loans held for portfolio	0	0
Loans held for sale	39,041	31,411
Derivative instruments	528	286
Accrued interest receivable	0	0
Financial Liabilities:
Deposits	779,535	924,955
Securities sold under agreements to repurchase	0	0
Accrued interest payable	0	0
Subordinated debentures	0	0
Liability for Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	0	0
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 3 [Member]
Financial Assets:
Cash and cash equivalents	0	0
Investment securities:
Available for sale	0	0
Held to maturity debt securities, fair value	0	0
Loans held for portfolio	3,350,710	2,937,948
Loans held for sale	0	0
Derivative instruments	0	0
Accrued interest receivable	0	0
Financial Liabilities:
Deposits	0	0
Securities sold under agreements to repurchase	0	0
Accrued interest payable	0	0
Subordinated debentures	272,928	303,191
Liability for Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	12	12
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Financial Assets:
Cash and cash equivalents	162,058	205,402
Investment securities:
Available for sale	1,329,957	1,445,689
Held to maturity debt securities, fair value	595,177	618,148
Loans held for portfolio	3,336,745	3,050,958
Loans held for sale	39,041	31,411
FRB and FHLB stock	30,707	30,458
Derivative instruments	528	286
Accrued interest receivable	16,764	15,064
Financial Liabilities:
Deposits	4,898,040	4,849,504
Securities sold under agreements to repurchase	31,672	64,875
Accrued interest payable	808	831
Subordinated debentures	354,343	354,286
Liability for Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	$ 12	$ 12