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ACQUISITIONS (Details) (USD $)
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3 Months Ended | 9 Months Ended | 12 Months Ended | 12 Months Ended | ||||||||
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Sep. 30, 2013
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Sep. 30, 2012
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Sep. 30, 2013
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Sep. 30, 2012
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Dec. 31, 2012
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Dec. 31, 2012
Core Deposits [Member]
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Jul. 31, 2013
Bank of America Agreement [Member]
Branch
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Dec. 31, 2012
HSBC and First Niagara [Member]
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Dec. 31, 2012
HSBC and First Niagara [Member]
Acquired Impaired Loans [Member]
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Dec. 31, 2012
HSBC and First Niagara [Member]
Acquired Non-Impaired Loans [Member]
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Jul. 20, 2012
HSBC Branch Agreement [Member]
Branch
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Sep. 07, 2012
First Niagara Branch Agreement [Member]
Branch
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| 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 | |||||||||||