INVESTMENT SECURITIES (Details) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2014 Position	Dec. 31, 2013 Position	Dec. 31, 2012
Available-for-Sale Portfolio [Abstract]
Amortized Cost		$ 2,397,886,000	$ 2,217,165,000
Gross Unrealized Gains		77,293,000	27,104,000
Gross Unrealized Losses		2,254,000	58,106,000
Estimated Fair value		2,472,925,000	2,186,163,000
Other Securities [Abstract]
Amortized Cost		40,049,000	32,562,000
Estimated Fair Value		40,049,000	32,562,000
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 Months		28	390
12 Months or Longer		71	17
Total		99	407
Available-for-Sale Securities, in Unrealized Loss Position, Fair value [Abstract]
Less than 12 Months		16,458,000	1,451,284,000
12 Months or Longer		166,383,000	16,397,000
Total		182,841,000	1,467,681,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 Months		35,000	56,464,000
12 Months or Longer		2,219,000	1,642,000
Total		2,254,000	58,106,000
Available-for-Sale Securities, Debt Maturities, Amortized Cost [Abstract]
Due in one year or less		59,386,000
Due in one to five years		146,559,000
Due in five through ten years		1,698,124,000
Due after ten years		247,266,000
Subtotal		2,151,335,000
Amortized Cost		2,397,636,000
Available-for-Sale Securities, Debt Maturities, Fair value [Abstract]
Due in one year or less		60,045,000
Due in one to five years		150,631,000
Due in five through ten years		1,746,688,000
Due after ten years		259,363,000
Subtotal		2,216,727,000
Fair Value		2,472,480,000
Pooled trust preferred, class A-1 securities, realized loss			15,500,000
Book value of U.S. Treasury securities held-to-maturity sold			417,600,000
Realized gains on held-to-maturity securities sold			32,400,000
Held-to-maturity transferred to available-for-sale, book value			198,900,000
Held-to-maturity transferred to available-for-sale, unrealized losses			1,800,000
U.S. Treasury and agency securities sold due to balance sheet restructuring	648,700,000
Gains on investment securities sold due to balance sheet restructuring	63,800,000
Cash flow information on investment securities [Abstract]
Gross gains on sales of investment securities		0	96,258,000	350,000
Gross losses on sales of investment securities		0	15,490,000	59,000
Proceeds from the maturities of mortgage-backed securities and CMO's		46,791,000	83,232,000	109,843,000
Purchases of mortgage backed securities and CMO's		22,234,000	51,194,000	26,292,000
Investment securities pledged to collateralize certain deposits and borrowings		1,182,000,000	978,000,000
U.S. Treasury and Agency Securities [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost		1,479,134,000	1,252,332,000
Gross Unrealized Gains		39,509,000	1,119,000
Gross Unrealized Losses		910,000	41,304,000
Estimated Fair value		1,517,733,000	1,212,147,000
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 Months		0	43
12 Months or Longer		4	0
Total		4	43
Available-for-Sale Securities, in Unrealized Loss Position, Fair value [Abstract]
Less than 12 Months		0	1,181,214,000
12 Months or Longer		102,363,000	0
Total		102,363,000	1,181,214,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 Months		0	41,304,000
12 Months or Longer		910,000	0
Total		910,000	41,304,000
Obligations of State and Political Subdivisions [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost		645,398,000	665,441,000
Gross Unrealized Gains		26,749,000	15,919,000
Gross Unrealized Losses		244,000	12,378,000
Estimated Fair value		671,903,000	668,982,000
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 Months		23	302
12 Months or Longer		46	9
Total		69	311
Available-for-Sale Securities, in Unrealized Loss Position, Fair value [Abstract]
Less than 12 Months		13,413,000	195,526,000
12 Months or Longer		26,490,000	4,974,000
Total		39,903,000	200,500,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 Months		34,000	11,774,000
12 Months or Longer		210,000	604,000
Total		244,000	12,378,000
Government Agency Mortgage-Backed Securities [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost		228,971,000	250,431,000
Gross Unrealized Gains		9,782,000	8,660,000
Gross Unrealized Losses		1,025,000	4,113,000
Estimated Fair value		237,728,000	254,978,000
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 Months		3	43
12 Months or Longer		19	6
Total		22	49
Available-for-Sale Securities, in Unrealized Loss Position, Fair value [Abstract]
Less than 12 Months		5,000	68,917,000
12 Months or Longer		34,770,000	8,713,000
Total		34,775,000	77,630,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 Months		0	3,262,000
12 Months or Longer		1,025,000	851,000
Total		1,025,000	4,113,000
Available-for-Sale Securities, Debt Maturities, Amortized Cost [Abstract]
Without single maturity date		228,971,000
Available-for-Sale Securities, Debt Maturities, Fair value [Abstract]
Without single maturity date		237,728,000
Corporate Debt Securities [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost		26,803,000	26,932,000
Gross Unrealized Gains		363,000	873,000
Gross Unrealized Losses		75,000	218,000
Estimated Fair value		27,091,000	27,587,000
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 Months		1	1
12 Months or Longer		1	1
Total		2	2
Available-for-Sale Securities, in Unrealized Loss Position, Fair value [Abstract]
Less than 12 Months		3,040,000	3,026,000
12 Months or Longer		2,755,000	2,703,000
Total		5,795,000	5,729,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 Months		1,000	31,000
12 Months or Longer		74,000	187,000
Total		75,000	218,000
Government Agency Collateralized Mortgage Obligations [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost		17,330,000	21,779,000
Gross Unrealized Gains		695,000	362,000
Gross Unrealized Losses		0	93,000
Estimated Fair value		18,025,000	22,048,000
Available-for-Sale Securities in Unrealized Loss Positions, Number of Positions [Abstract]
Less than 12 Months		1	1
12 Months or Longer		1	1
Total		2	2
Available-for-Sale Securities, in Unrealized Loss Position, Fair value [Abstract]
Less than 12 Months		0	2,601,000
12 Months or Longer		5,000	7,000
Total		5,000	2,608,000
Available-for-Sale Securities, in Unrealized Loss Position, Gross Unrealized Losses [Abstract]
Less than 12 Months		0	93,000
12 Months or Longer		0	0
Total		0	93,000
Available-for-Sale Securities, Debt Maturities, Amortized Cost [Abstract]
Without single maturity date		17,330,000
Available-for-Sale Securities, Debt Maturities, Fair value [Abstract]
Without single maturity date		18,025,000
Marketable Equity Security [Member]
Available-for-Sale Portfolio [Abstract]
Amortized Cost		250,000	250,000
Gross Unrealized Gains		195,000	171,000
Gross Unrealized Losses		0	0
Estimated Fair value		445,000	421,000
Federal Home Loan Bank Common Stock [Member]
Other Securities [Abstract]
Amortized Cost		19,553,000	12,053,000
Estimated Fair Value		19,553,000	12,053,000
Federal Reserve Bank Common Stock [Member]
Other Securities [Abstract]
Amortized Cost		16,050,000	16,050,000
Estimated Fair Value		16,050,000	16,050,000
Other Equity Securities [Member]
Other Securities [Abstract]
Amortized Cost		4,446,000	4,459,000
Estimated Fair Value		$ 4,446,000	$ 4,459,000