INVESTMENT SECURITIES (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014 Position	Dec. 31, 2013 Position
Available-for-Sale Portfolio [Abstract]
Amortized Cost	$ 2,421,718	$ 2,217,165
Gross Unrealized Gains	54,375	27,104
Gross Unrealized Losses	10,162	58,106
Fair Value	2,465,931	2,186,163
Other Securities [Abstract]
Amortized Cost	40,311	32,562
Fair Value	40,311	32,562
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Available-for-sale/investment portfolio in unrealized loss positions less than 12 months qualitative disclosure, number of positions	47	390
Available-for-sale/investment portfolio in unrealized loss positions for 12 months or longer, number of positions	114	17
Total available-for-sale/investment portfolio in unrealized loss positions, number of positions	161	407
Available-for-Sale Portfolio, Debt Maturities, Fair Value [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, fair value	187,105	1,451,284
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, fair value	332,023	16,397
Total available-for-sale/investment portfolio, unrealized loss position, fair value	519,128	1,467,681
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, gross unrealized losses	984	56,464
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, gross unrealized losses	9,178	1,642
Total Available-for-sale/investment portfolio, unrealized loss position, gross unrealized losses	10,162	58,106
Available-for-Sale, Amortized Cost [Abstract]
Available-for-sale, amortized cost, due in one year or less	49,520
Available-for-sale, amortized cost, due in one to five years	156,732
Available-for-sale, amortized cost, due in five through ten years	1,691,095
Available-for-sale, amortized cost, due after ten years	268,908
Available-for-sale, amortized cost, with a single maturity date, subtotal	2,166,255
Available-for-sale, government agency mortgage-backed securities, amortized cost, without a single maturity date	236,819
Available-for-sale, government agency collateralized mortgage obligations, amortized cost, without a single maturity date	18,394
Available-for-sale, amortized cost	2,421,468
Available-for-Sale, Fair Value [Abstract]
Available-for-sale, fair value, due in one year or less	50,144
Available-for-sale, fair value, due in one to five years	161,940
Available-for-sale, fair value, due in five through ten years	1,710,084
Available-for-sale, fair value, due after ten years	280,080
Available-for-sale, fair value with a single maturity date, subtotal	2,202,248
Available-for-sale, government agency mortgage-backed securities, fair value, without single maturity date	244,122
Available-for-sale, government agency collateralized mortgage obligations, fair value, without single maturity date	19,130
Available-for-sale, fair value	2,465,500
U.S. Treasury and Agency Obligations [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost	1,476,678	1,252,332
Gross Unrealized Gains	17,210	1,119
Gross Unrealized Losses	7,261	41,304
Fair Value	1,486,627	1,212,147
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Available-for-sale/investment portfolio in unrealized loss positions less than 12 months qualitative disclosure, number of positions	7	43
Available-for-sale/investment portfolio in unrealized loss positions for 12 months or longer, number of positions	10	0
Total available-for-sale/investment portfolio in unrealized loss positions, number of positions	17	43
Available-for-Sale Portfolio, Debt Maturities, Fair Value [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, fair value	158,289	1,181,214
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, fair value	230,998	0
Total available-for-sale/investment portfolio, unrealized loss position, fair value	389,287	1,181,214
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, gross unrealized losses	859	41,304
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, gross unrealized losses	6,402	0
Total Available-for-sale/investment portfolio, unrealized loss position, gross unrealized losses	7,261	41,304
Obligations of State and Political Subdivisions [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost	662,742	665,441
Gross Unrealized Gains	26,621	15,919
Gross Unrealized Losses	1,029	12,378
Fair Value	688,334	668,982
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Available-for-sale/investment portfolio in unrealized loss positions less than 12 months qualitative disclosure, number of positions	31	302
Available-for-sale/investment portfolio in unrealized loss positions for 12 months or longer, number of positions	78	9
Total available-for-sale/investment portfolio in unrealized loss positions, number of positions	109	311
Available-for-Sale Portfolio, Debt Maturities, Fair Value [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, fair value	16,009	195,526
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, fair value	49,434	4,974
Total available-for-sale/investment portfolio, unrealized loss position, fair value	65,443	200,500
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, gross unrealized losses	78	11,774
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, gross unrealized losses	951	604
Total Available-for-sale/investment portfolio, unrealized loss position, gross unrealized losses	1,029	12,378
Government Agency Mortgage-Backed Securities [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost	236,819	250,431
Gross Unrealized Gains	9,088	8,660
Gross Unrealized Losses	1,785	4,113
Fair Value	244,122	254,978
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Available-for-sale/investment portfolio in unrealized loss positions less than 12 months qualitative disclosure, number of positions	8	43
Available-for-sale/investment portfolio in unrealized loss positions for 12 months or longer, number of positions	24	6
Total available-for-sale/investment portfolio in unrealized loss positions, number of positions	32	49
Available-for-Sale Portfolio, Debt Maturities, Fair Value [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, fair value	12,807	68,917
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, fair value	48,830	8,713
Total available-for-sale/investment portfolio, unrealized loss position, fair value	61,637	77,630
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, gross unrealized losses	47	3,262
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, gross unrealized losses	1,738	851
Total Available-for-sale/investment portfolio, unrealized loss position, gross unrealized losses	1,785	4,113
Corporate Debt Securities [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost	26,835	26,932
Gross Unrealized Gains	539	873
Gross Unrealized Losses	87	218
Fair Value	27,287	27,587
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Available-for-sale/investment portfolio in unrealized loss positions less than 12 months qualitative disclosure, number of positions	0	1
Available-for-sale/investment portfolio in unrealized loss positions for 12 months or longer, number of positions	1	1
Total available-for-sale/investment portfolio in unrealized loss positions, number of positions	1	2
Available-for-Sale Portfolio, Debt Maturities, Fair Value [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, fair value	0	3,026
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, fair value	2,756	2,703
Total available-for-sale/investment portfolio, unrealized loss position, fair value	2,756	5,729
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, gross unrealized losses	0	31
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, gross unrealized losses	87	187
Total Available-for-sale/investment portfolio, unrealized loss position, gross unrealized losses	87	218
Government Agency Collateralized Mortgage Obligations [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost	18,394	21,779
Gross Unrealized Gains	736	362
Gross Unrealized Losses	0	93
Fair Value	19,130	22,048
Available-for-Sale Portfolio in Unrealized Loss Positions, Number of Positions [Abstract]
Available-for-sale/investment portfolio in unrealized loss positions less than 12 months qualitative disclosure, number of positions	1	1
Available-for-sale/investment portfolio in unrealized loss positions for 12 months or longer, number of positions	1	1
Total available-for-sale/investment portfolio in unrealized loss positions, number of positions	2	2
Available-for-Sale Portfolio, Debt Maturities, Fair Value [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, fair value	0	2,601
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, fair value	5	7
Total available-for-sale/investment portfolio, unrealized loss position, fair value	5	2,608
Available-for-Sale Portfolio, Debt Maturities, Gross Unrealized Losses [Abstract]
Available-for-sale/investment portfolio, unrealized loss position, less than 12 months, gross unrealized losses	0	93
Available-for-sale/investment portfolio, unrealized loss position, 12 months or longer, gross unrealized losses	0	0
Total Available-for-sale/investment portfolio, unrealized loss position, gross unrealized losses	0	93
Marketable Equity Securities [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost	250	250
Gross Unrealized Gains	181	171
Gross Unrealized Losses	0	0
Fair Value	431	421
Federal Home Loan Bank Common Stock [Member]
Other Securities [Abstract]
Amortized Cost	19,814	12,053
Fair Value	19,814	12,053
Federal Reserve Bank Common Stock [Member]
Other Securities [Abstract]
Amortized Cost	16,050	16,050
Fair Value	16,050	16,050
Other Equity Securities [Member]
Other Securities [Abstract]
Amortized Cost	4,447	4,459
Fair Value	$ 4,447	$ 4,459