FAIR VALUE DISCLOSURES (Estimated Fair Value of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Investment securities:
Available for sale	$ 1,461,552	$ 1,611,745
Held-to-maturity Securities, Fair Value	658,343	719,183
FRB and FHLB stock	30,623	27,357
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Assets:
Cash and cash equivalents	263,466	190,435
Investment securities:
Available for sale	1,461,552	1,611,745
Held-to-maturity Securities, Fair Value	658,343	719,183
Loans held for portfolio	2,768,334	2,562,160
Loans held for sale	28,866	25,548
FRB and FHLB stock	30,623	27,357
Derivative instruments	228	513
Accrued interest receivable	15,400	17,798
Financial Liabilities:
Deposits	4,826,276	4,814,267
Securities sold under agreements to repurchase	42,682	43,143
Accrued interest payable	789	63,341
Subordinated debentures	302,041	242,678
Off-Balance Sheet Financial Instruments:
Liability for commitments to extend credit, standby letters of credit and financial guarantees	2,430	2,715
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash and cash equivalents	263,466	190,435
Investment securities:
Available for sale	1,709	1,443
Held-to-maturity Securities, Fair Value	0	0
Loans held for portfolio	0	0
Loans held for sale	0	0
FRB and FHLB stock	30,623	27,357
Derivative instruments	0	0
Accrued interest receivable	15,400	17,798
Financial Liabilities:
Deposits	3,880,285	3,767,782
Securities sold under agreements to repurchase	42,682	43,143
Accrued interest payable	789	63,341
Subordinated debentures	0	0
Off-Balance Sheet Financial Instruments:
Liability for 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	1,459,843	1,610,302
Held-to-maturity Securities, Fair Value	658,343	719,183
Loans held for portfolio	0	0
Loans held for sale	28,866	25,548
FRB and FHLB stock	0	0
Derivative instruments	228	513
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	0	0
Off-Balance Sheet Financial Instruments:
Liability for 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 Securities, Fair Value	0	0
Loans held for portfolio	2,768,334	2,562,160
Loans held for sale	0	0
FRB and FHLB stock	0	0
Derivative instruments	0	0
Accrued interest receivable	0	0
Financial Liabilities:
Deposits	945,991	1,046,485
Securities sold under agreements to repurchase	0	0
Accrued interest payable	0	0
Subordinated debentures	302,041	242,678
Off-Balance Sheet Financial Instruments:
Liability for commitments to extend credit, standby letters of credit and financial guarantees	2,430	2,715
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Financial Assets:
Cash and cash equivalents	263,466	190,435
Investment securities:
Available for sale	1,461,552	1,611,745
Held-to-maturity Securities, Fair Value	667,831	740,186
Loans held for portfolio	2,876,017	2,750,514
Loans held for sale	28,866	25,548
FRB and FHLB stock	30,623	27,357
Derivative instruments	228	513
Accrued interest receivable	15,400	17,798
Financial Liabilities:
Deposits	4,826,930	4,813,895
Securities sold under agreements to repurchase	42,682	43,143
Accrued interest payable	789	63,341
Subordinated debentures	354,267	354,210
Off-Balance Sheet Financial Instruments:
Liability for commitments to extend credit, standby letters of credit and financial guarantees	$ 2,430	$ 2,715