DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES (Details) (USD $)	3 Months Ended		6 Months Ended			3 Months Ended					6 Months Ended			3 Months Ended				6 Months Ended		3 Months Ended		6 Months Ended			12 Months Ended	3 Months Ended		6 Months Ended			12 Months Ended				6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended			6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended			6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended			6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended			6 Months Ended	12 Months Ended	3 Months Ended		6 Months Ended			6 Months Ended	12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Mar. 31, 2014 FHLBB borrowings	Jun. 30, 2014 Cash flow hedges	Dec. 31, 2013 Cash flow hedges	Jun. 30, 2014 Economic hedges	Dec. 31, 2013 Economic hedges	Jun. 30, 2014 Economic hedges Tax advantaged economic development bonds	Jun. 30, 2014 Non-hedging derivatives	Dec. 31, 2013 Non-hedging derivatives	Mar. 31, 2014 Interest rate swaps FHLBB borrowings	Mar. 31, 2014 Interest rate swaps 90 day rolling FHLB advances	Jun. 30, 2014 Interest rate swaps Cash flow hedges	Jun. 30, 2013 Interest rate swaps Cash flow hedges	Jun. 30, 2014 Interest rate swaps Cash flow hedges	Jun. 30, 2013 Interest rate swaps Cash flow hedges	Jun. 30, 2014 Interest rate swaps Cash flow hedges FHLBB borrowings	Jun. 30, 2013 Interest rate swaps Cash flow hedges FHLBB borrowings	Jun. 30, 2014 Interest rate swaps Cash flow hedges FHLBB borrowings	Jun. 30, 2013 Interest rate swaps Cash flow hedges FHLBB borrowings	Dec. 31, 2013 Interest rate swaps Cash flow hedges FHLBB borrowings	Dec. 31, 2013 Interest rate swaps Cash flow hedges FHLBB borrowings Weighted Average	Jun. 30, 2014 Interest rate swaps Cash flow hedges Junior subordinated notes	Jun. 30, 2013 Interest rate swaps Cash flow hedges Junior subordinated notes	Jun. 30, 2014 Interest rate swaps Cash flow hedges Junior subordinated notes	Jun. 30, 2013 Interest rate swaps Cash flow hedges Junior subordinated notes	Dec. 31, 2013 Interest rate swaps Cash flow hedges Junior subordinated notes	Dec. 31, 2013 Interest rate swaps Cash flow hedges Junior subordinated notes Weighted Average	Jun. 30, 2014 Interest rate swaps Economic hedges	Jun. 30, 2014 Interest rate swaps Economic hedges Tax advantaged economic development bonds	Dec. 31, 2013 Interest rate swaps Economic hedges Tax advantaged economic development bonds	Jun. 30, 2014 Interest rate swaps Economic hedges Tax advantaged economic development bonds Weighted Average	Dec. 31, 2013 Interest rate swaps Economic hedges Tax advantaged economic development bonds Weighted Average	Jun. 30, 2014 Interest rate swaps Economic hedges Loans with commercial loan customers	Jun. 30, 2013 Interest rate swaps Economic hedges Loans with commercial loan customers	Jun. 30, 2014 Interest rate swaps Economic hedges Loans with commercial loan customers	Jun. 30, 2013 Interest rate swaps Economic hedges Loans with commercial loan customers	Dec. 31, 2013 Interest rate swaps Economic hedges Loans with commercial loan customers	Jun. 30, 2014 Interest rate swaps Economic hedges Loans with commercial loan customers Weighted Average	Dec. 31, 2013 Interest rate swaps Economic hedges Loans with commercial loan customers Weighted Average	Jun. 30, 2014 Interest rate swaps Economic hedges Industrial revenue bond	Jun. 30, 2013 Interest rate swaps Economic hedges Industrial revenue bond	Jun. 30, 2014 Interest rate swaps Economic hedges Industrial revenue bond	Jun. 30, 2013 Interest rate swaps Economic hedges Industrial revenue bond	Mar. 31, 2014 Forward-starting interest rate swaps 90 day rolling FHLB advances	Jun. 30, 2014 Forward-starting interest rate swaps Cash flow hedges item	Jun. 30, 2014 Forward-starting interest rate swaps Cash flow hedges FHLBB borrowings	Dec. 31, 2013 Forward-starting interest rate swaps Cash flow hedges FHLBB borrowings	Jun. 30, 2014 Forward-starting interest rate swaps Cash flow hedges FHLBB borrowings Weighted Average	Dec. 31, 2013 Forward-starting interest rate swaps Cash flow hedges FHLBB borrowings Weighted Average	Jun. 30, 2014 Reverse interest rate swaps Economic hedges Loans with commercial loan customers	Jun. 30, 2013 Reverse interest rate swaps Economic hedges Loans with commercial loan customers	Jun. 30, 2014 Reverse interest rate swaps Economic hedges Loans with commercial loan customers	Jun. 30, 2013 Reverse interest rate swaps Economic hedges Loans with commercial loan customers	Dec. 31, 2013 Reverse interest rate swaps Economic hedges Loans with commercial loan customers	Jun. 30, 2014 Reverse interest rate swaps Economic hedges Loans with commercial loan customers Weighted Average	Dec. 31, 2013 Reverse interest rate swaps Economic hedges Loans with commercial loan customers Weighted Average	Jun. 30, 2014 Interest rate lock commitments Non-hedging derivatives	Jun. 30, 2013 Interest rate lock commitments Non-hedging derivatives	Jun. 30, 2014 Interest rate lock commitments Non-hedging derivatives	Jun. 30, 2013 Interest rate lock commitments Non-hedging derivatives	Dec. 31, 2013 Interest rate lock commitments Non-hedging derivatives	Jun. 30, 2014 Interest rate lock commitments Non-hedging derivatives Weighted Average	Dec. 31, 2013 Interest rate lock commitments Non-hedging derivatives Weighted Average	Jun. 30, 2014 Forward sale commitments Economic hedges	Jun. 30, 2013 Forward sale commitments Economic hedges	Jun. 30, 2014 Forward sale commitments Economic hedges	Jun. 30, 2013 Forward sale commitments Economic hedges	Dec. 31, 2013 Forward sale commitments Economic hedges	Jun. 30, 2014 Forward sale commitments Economic hedges Weighted Average	Dec. 31, 2013 Forward sale commitments Economic hedges Weighted Average
Derivative instruments and hedging activities
Cash pledged as collateral to derivative counterparties	$ 1,800,000		$ 1,800,000
Amortized cost of securities pledged as collateral to derivative counterparties	24,400,000		24,400,000
Fair value of securities as pledged collateral to derivative counterparties	24,800,000		24,800,000
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	911,888,000		911,888,000		905,071,000		300,000,000	425,000,000	571,497,000	459,872,000		40,391,000	20,199,000											150,000,000						15,000,000		518,600,000	12,827,000	13,095,000			252,874,000		252,874,000		206,933,000									300,000,000	260,000,000			252,874,000		252,874,000		206,933,000			40,391,000		40,391,000		20,199,000			52,922,000		52,922,000		32,911,000
Weighted Average Maturity																									2 years 6 months						4 months 24 days				15 years 4 months 24 days	15 years 10 months 24 days						5 years 10 months 24 days	5 years 4 months 24 days									4 years 9 months 18 days	4 years 6 months						5 years 10 months 24 days	5 years 4 months 24 days						2 months 12 days	2 months 12 days						2 months 12 days	2 months 12 days
Weighted Average Rate, Received (as a percent)																								0.25%						2.09%			0.52%	0.54%			2.34%		2.34%		2.44%									0.00%				4.58%		4.58%		4.68%
Weighted Average Rate, Contract pay rate (as a percent)																								2.61%						5.54%			5.09%	5.09%			4.58%		4.58%		4.68%									2.29%	1.88%			2.34%		2.34%		2.44%
Estimated Fair Value Asset (Liability)	(3,216,000)		(3,216,000)		(3,652,000)		(1,022,000)	(2,290,000)	(2,854,000)	(1,620,000)		660,000	258,000											(3,102,000)						(203,000)			(2,322,000)	(1,889,000)			(9,193,000)		(9,193,000)		(6,278,000)									(1,022,000)	1,015,000			9,222,000		9,222,000		6,286,000			660,000		660,000		258,000			(561,000)		(561,000)		261,000
Cash flow hedges:
Number of instruments																																																	6
Durations of derivative instruments																																																	3 years
Interest rate swaps on FHLBB borrowings:
Unrealized (loss) gain recognized in accumulated other comprehensive loss																				(3,343,000)	5,131,000	(4,127,000)	5,437,000				(4,000)	(1,000)	(5,000)
Reclassification of unrealized (loss) gain from accumulated other comprehensive loss to interest expense	6,846,000	8,593,000	13,875,000	17,537,000																	899,000		1,910,000			75,000	129,000	204,000	256,000
Reclassification of unrealized loss from accumulated other comprehensive loss to other non-interest income for termination of swaps																					236,000	8,630,000	472,000
Reclassification of unrealized deferred tax benefit from accumulated other comprehensive loss to tax expense for terminated swaps																					(95,000)	(3,611,000)	(303,000)
Net tax benefit (expense) on items recognized in accumulated other comprehensive loss																				1,352,000	(2,433,000)	1,666,000	(2,955,000)			(29,000)	(48,000)	(80,000)	(102,000)
Other comprehensive income recorded in accumulated other comprehensive loss, net of reclassification adjustments and tax effects																(1,945,000)	3,815,000	2,681,000	4,710,000
Net interest expense recognized in interest expense	2,368,000	3,541,000	4,676,000	7,122,000																	1,076,000		2,319,000			75,000	129,000	204,000	256,000
Notional amount of derivative contract terminated														30,000,000	145,000,000																																	235,000,000
Extinguishment of FHLB advances						215,000,000
Loss reclassified from the effective portion of the unrealized changes in the fair value of the derivatives						8,600,000
Fixed rate of interest (as a percent)											5.09%
Life of the bond											21 years
Credit valuation adjustments									28,400
Economic hedges and non-hedging derivatives
Unrealized (loss) gain recognized in other non-interest income																																					(1,919,000)	4,996,000	(1,732,000)	6,550,000				(350,000)	665,000	(731,000)	772,000							1,919,000	(4,996,000)	1,732,000	(6,550,000)				660,000	(1,507,000)	1,037,000	1,251,000				(561,000)	4,913,000	(669,000)	4,363,000
Favorable change in credit valuation adjustment recognized in other non-interest income																																																						4,000	259,000	11,000	337,000
Realized gain (loss) in other non-interest income																																																													$ 769,000	$ 2,758,000	$ 1,035,000	$ 3,998,000				$ (177,000)	$ 517,000	$ (341,000)	$ 1,572,000