ACQUISITIONS (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 13, 2013 Branch	Sep. 07, 2012 Branch	Jul. 20, 2012 Branch
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Goodwill	$ 375,174,000	$ 374,991,000	$ 369,703,000
Summary of loans acquired [Abstract]
Merger and acquisition integration related expenses	100,000	2,200,000	5,700,000
Minimum [Member] | Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	7 years
Minimum [Member] | Core Deposits From Acquisitions [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	8 years
Minimum [Member] | Other Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	8 years
Maximum [Member] | Core Deposits [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	20 years
Maximum [Member] | Core Deposits From Acquisitions [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	10 years
Maximum [Member] | Other Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Estimated useful life	10 years
EBS-RMSCO, Inc. [Member]
Business Acquisition [Line Items]
Incremental revenue	1,200,000
Consideration paid (received) [Abstract]
Cash/Total net consideration paid (received)	924,000
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Cash and cash equivalents	0
Investment securities	0
Loans	0
Premises and equipment	0
Accrued interest receivable	0
Other assets/(liabilities), net	163,000
Core deposit intangibles	0
Other intangibles	578,000
Deposits	0
Borrowings	0
Total identifiable assets (liabilities), net	741,000
Goodwill	183,000
Bank of America Agreement [Member]
Business Acquisition [Line Items]
Number of new branch locations included in acquisition or purchase agreement				8
Loans acquired				1,000,000
Deposits acquired				303,000,000
Blended deposit premium (in hundredths)				2.40%
Total deposit premium paid				7,300,000
Consideration paid (received) [Abstract]
Cash/Total net consideration paid (received)		(291,980,000)
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Cash and cash equivalents		0
Investment securities		0
Loans		1,106,000
Premises and equipment		2,549,000
Accrued interest receivable		5,000
Other assets/(liabilities), net		(18,000)
Core deposit intangibles		2,537,000
Other intangibles		9,000
Deposits		(303,456,000)
Borrowings		0
Total identifiable assets (liabilities), net		(297,268,000)
Goodwill		5,288,000
First Niagara Branch Agreement [Member]
Business Acquisition [Line Items]
Number of new branch locations included in acquisition or purchase agreement					3
Loans acquired					54,000,000
Deposits acquired					101,000,000
Blended deposit premium (in hundredths)					3.10%
Total deposit premium paid					3,000,000
HSBC Branch Agreement [Member]
Business Acquisition [Line Items]
Number of new branch locations included in acquisition or purchase agreement						16
Loans acquired						106,000,000
Deposits acquired						697,000,000
Blended deposit premium (in hundredths)						3.40%
Total deposit premium paid						24,000,000
HSBC and First Niagara [Member]
Consideration paid (received) [Abstract]
Cash/Total net consideration paid (received)			(595,462,000)
Recognized amounts of identifiable assets acquired and liabilities assumed [Abstract]
Cash and cash equivalents			5,510,000
Investment securities			0
Loans			160,116,000
Premises and equipment			4,941,000
Accrued interest receivable			588,000
Other assets/(liabilities), net			171,000
Core deposit intangibles			6,521,000
Other intangibles			0
Deposits			(797,962,000)
Borrowings			0
Total identifiable assets (liabilities), net			(620,115,000)
Goodwill			24,653,000
Summary of loans acquired [Abstract]
Contractually required principal and interest at acquisition						201,745,000
Contractual cash flows not expected to be collected						(3,555,000)
Expected cash flows at acquisition						198,190,000
Interest component of expected cash flows						(38,074,000)
Fair value of acquired loans						160,116,000
HSBC and First Niagara [Member] | Acquired Impaired Loans [Member]
Summary of loans acquired [Abstract]
Contractually required principal and interest at acquisition						0
Contractual cash flows not expected to be collected						0
Expected cash flows at acquisition						0
Interest component of expected cash flows						0
Fair value of acquired loans						0
HSBC and First Niagara [Member] | Acquired Non-Impaired Loans [Member]
Summary of loans acquired [Abstract]
Contractually required principal and interest at acquisition						201,745,000
Contractual cash flows not expected to be collected						(3,555,000)
Expected cash flows at acquisition						198,190,000
Interest component of expected cash flows						(38,074,000)
Fair value of acquired loans						$ 160,116,000