FAIR VALUE DISCLOSURES (Estimated Fair Values of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investment securities [Abstract]
Available for sale	$ 1,408,172	$ 1,611,745
Held to maturity	704,977	719,183
Estimate of Fair Value, Fair Value Disclosure [Member]
Financial Assets:
Cash and cash equivalents	341,235	190,435
Investment securities [Abstract]
Available for sale	1,408,172	1,611,745
Held to maturity	704,977	719,183
Loans held for portfolio	2,683,895	2,562,160
Loans held for sale	21,402	25,548
FRB and FHLB stock	32,148	27,357
Derivative instruments	346	513
Accrued interest receivable	16,087	17,798
Financial Liabilities:
Noninterest-bearing demand	1,273,662	1,243,545
Interest-bearing demand	699,158	679,527
Savings and money market	1,841,905	1,844,710
Time deposits	1,027,869	1,046,485
Securities sold under agreements to repurchase	36,713	43,143
Accrued interest payable	656	63,341
Subordinated debentures	287,981	242,678
Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	(2,715)	(2,715)
Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Inputs, Level 1 [Member]
Financial Assets:
Cash and cash equivalents	341,235	190,435
Investment securities [Abstract]
Available for sale	1,691	1,443
Held to maturity	0	0
Loans held for portfolio	0	0
Loans held for sale	0	0
FRB and FHLB stock	32,148	27,357
Derivative instruments	0	0
Accrued interest receivable	16,087	17,798
Financial Liabilities:
Noninterest-bearing demand	1,273,662	1,243,545
Interest-bearing demand	699,158	679,527
Savings and money market	1,841,905	1,844,710
Time deposits	0	0
Securities sold under agreements to repurchase	36,713	43,143
Accrued interest payable	656	63,341
Subordinated debentures	0	0
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 [Abstract]
Available for sale	1,406,481	1,610,302
Held to maturity	704,977	719,183
Loans held for portfolio	0	0
Loans held for sale	21,402	25,548
FRB and FHLB stock	0	0
Derivative instruments	346	513
Accrued interest receivable	0	0
Financial Liabilities:
Noninterest-bearing demand	0	0
Interest-bearing demand	0	0
Savings and money market	0	0
Time 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:
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 [Abstract]
Available for sale	0	0
Held to maturity	0	0
Loans held for portfolio	2,683,895	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:
Noninterest-bearing demand	0	0
Interest-bearing demand	0	0
Savings and money market	0	0
Time deposits	1,027,869	1,046,485
Securities sold under agreements to repurchase	0	0
Accrued interest payable	0	0
Subordinated debentures	287,981	242,678
Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	(2,715)	(2,715)
Carrying (Reported) Amount, Fair Value Disclosure [Member]
Financial Assets:
Cash and cash equivalents	341,235	190,435
Investment securities [Abstract]
Available for sale	1,408,172	1,611,745
Held to maturity	718,672	740,186
Loans held for portfolio	2,789,748	2,750,514
Loans held for sale	21,402	25,548
FRB and FHLB stock	32,148	27,357
Derivative instruments	346	513
Accrued interest receivable	16,087	17,798
Financial Liabilities:
Noninterest-bearing demand	1,273,662	1,243,545
Interest-bearing demand	699,158	679,527
Savings and money market	1,841,905	1,844,710
Time deposits	1,027,706	1,046,113
Securities sold under agreements to repurchase	36,713	43,143
Accrued interest payable	656	63,341
Subordinated debentures	354,229	354,210
Off-Balance Sheet Financial Instruments:
Commitments to extend credit, standby letters of credit and financial guarantees	$ (2,715)	$ (2,715)