FAIR VALUE DISCLOSURES (Estimated Fair Value of Financial Instruments) (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Investment securities:
Available for sale	$ 1,501,503	$ 1,445,689
Held to maturity debt securities, fair value	583,670	614,272
FRB and FHLB stock	30,390	30,458
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Assets:
Cash and cash equivalents	238,356	205,402
Investment securities:
Available for sale	1,501,503	1,445,689
Held to maturity debt securities, fair value	583,670	614,272
Loans held for portfolio	3,252,942	2,937,948
Loans held for sale	36,428	31,411
Derivative instruments	1,103	286
Accrued interest receivable	15,206	15,064
Financial Liabilities:
Deposits	5,055,442	4,848,582
Securities sold under agreements to repurchase	45,616	64,875
Accrued interest payable	842	831
Subordinated debentures	273,116	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	238,356	205,402
Investment securities:
Available for sale	1,956	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	15,206	15,064
Financial Liabilities:
Deposits	4,180,414	3,923,627
Securities sold under agreements to repurchase	45,616	64,875
Accrued interest payable	842	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	1,499,547	1,443,722
Held to maturity debt securities, fair value	583,670	614,272
Loans held for portfolio	0	0
Loans held for sale	36,428	31,411
Derivative instruments	1,103	286
Accrued interest receivable	0	0
Financial Liabilities:
Deposits	875,028	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	3,252,942	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	273,116	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	238,356	205,402
Investment securities:
Available for sale	1,501,503	1,445,689
Held to maturity debt securities, fair value	587,200	618,148
Loans held for portfolio	3,249,663	3,050,958
Loans held for sale	36,428	31,411
FRB and FHLB stock	30,390	30,458
Derivative instruments	1,103	286
Accrued interest receivable	15,206	15,064
Financial Liabilities:
Deposits	5,056,525	4,849,504
Securities sold under agreements to repurchase	45,616	64,875
Accrued interest payable	842	831
Subordinated debentures	354,324	354,286
Liability for Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	$ 12	$ 12