ACQUISITIONS (Details) (USD $)	3 Months Ended		9 Months Ended			12 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2012 Core Deposits [Member]	Jul. 31, 2013 Bank of America Agreement [Member] Branch	Dec. 31, 2012 HSBC and First Niagara [Member]	Dec. 31, 2012 HSBC and First Niagara [Member] Acquired Impaired Loans [Member]	Dec. 31, 2012 HSBC and First Niagara [Member] Acquired Non-Impaired Loans [Member]	Jul. 20, 2012 HSBC Branch Agreement [Member] Branch	Sep. 07, 2012 First Niagara Branch Agreement [Member] Branch
Business Acquisition [Line Items]
Number of new branch locations included in acquisition or purchase agreement							8				16	3
Loans acquired							$ 1,000,000				$ 106,000,000	$ 54,000,000
Deposits acquired							340,000,000				697,000,000	101,000,000
Blended deposit premium (in hundredths)							2.40%				3.40%	3.10%
Total deposit premium paid											24,000,000	3,000,000
Consideration received [Abstract]
Cash/Total net consideration received								(595,462,000)
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Cash and cash equivalents								5,510,000
Loans								160,116,000
Premises and equipment								4,941,000
Accrued interest receivable								588,000
Other assets and liabilities, net								171,000
Core deposit intangibles								6,521,000
Deposits								(797,962,000)
Total identifiable liabilities, net								(620,115,000)
Goodwill	369,703,000	369,703,000	369,703,000	369,703,000	369,703,000			24,653,000
Summary of loans acquired [Abstract]
Contractually required principal and interest at acquisition								201,745,000	0	201,745,000
Contractual cash flows not expected to be collected								(3,555,000)	0	(3,555,000)
Expected cash flows at acquisition								198,190,000	0	198,190,000
Interest component of expected cash flows								(38,074,000)	0	(38,074,000)
Fair value of acquired loans								160,116,000	0	160,116,000
Merger and acquisition integration related expenses	$ 100,000	$ 4,800,000	$ 100,000	$ 5,200,000
Finite-Lived Intangible Assets [Line Items]
Estimated useful life of core deposit intangible and other intangible						8 years