OPERATING SEGMENTS (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 segment	Dec. 31, 2013	Dec. 31, 2012
Operating segments
Number of reportable operating segments									2
Net interest income	$ 46,647,000	$ 44,949,000	$ 44,329,000	$ 42,766,000	$ 39,842,000	$ 45,869,000	$ 41,104,000	$ 41,937,000	$ 178,691,000	$ 168,752,000	$ 143,388,000
Provision for loan losses	3,898,000	3,685,000	3,989,000	3,396,000	3,100,000	3,178,000	2,700,000	2,400,000	14,968,000	11,378,000	9,590,000
Non-interest income	14,200,000	14,641,000	14,506,000	4,423,000	15,714,000	12,114,000	15,606,000	14,798,000	47,770,000	58,232,000	54,056,000
Non-interest expense	41,676,000	39,687,000	39,263,000	45,360,000	37,157,000	42,784,000	37,935,000	39,483,000	165,986,000	157,359,000	140,806,000
Income from continuing operations before income taxes	15,273,000	16,218,000	15,583,000	(1,567,000)	15,299,000	12,021,000	16,075,000	14,852,000	45,507,000	58,247,000	47,048,000
Income tax expense (benefit)	3,875,000	4,230,000	4,119,000	(461,000)	4,762,000	3,917,000	4,038,000	4,387,000	11,763,000	17,104,000	13,223,000
Net income from continuing operations	11,398,000	11,988,000	11,464,000	(1,106,000)	10,537,000	8,104,000	12,037,000	10,465,000	33,744,000	41,143,000	33,825,000
Loss from discontinued operations before income taxes (including gain on disposal of$63)											(261,000)
Gain on disposal											63,000
Income tax benefit											376,000
Net loss from discontinued operations											(637,000)
Net income	11,398,000	11,988,000	11,464,000	(1,106,000)	10,537,000	8,104,000	12,037,000	10,465,000	33,744,000	41,143,000	33,188,000
Average assets (in millions)									6,171,000,000	5,307,000,000	5,203,000,000
Operating segment | Banking
Operating segments
Net interest income									182,221,000	172,634,000	145,167,000
Provision for loan losses									14,968,000	11,378,000	9,590,000
Non-interest income									37,406,000	48,238,000	43,330,000
Non-interest expense									155,642,000	146,944,000	128,366,000
Income from continuing operations before income taxes									49,017,000	62,550,000	50,541,000
Income tax expense (benefit)									13,085,000	18,802,000	14,597,000
Net income from continuing operations											35,944,000
Loss from discontinued operations before income taxes (including gain on disposal of$63)											(261,000)
Gain on disposal											63,000
Income tax benefit											376,000
Net loss from discontinued operations											(637,000)
Net income									35,932,000	43,748,000	35,307,000
Average assets (in millions)									6,149,000,000	5,279,000,000	5,006,000,000
Operating segment | Insurance
Operating segments
Non-interest income									10,364,000	9,994,000	10,726,000
Non-interest expense									8,058,000	8,069,000	8,452,000
Income from continuing operations before income taxes									2,306,000	1,925,000	2,274,000
Income tax expense (benefit)									1,008,000	759,000	903,000
Net income from continuing operations											1,371,000
Net income									1,298,000	1,166,000	1,371,000
Average assets (in millions)									27,000,000	27,000,000	30,000,000
Reportable legal entity | Berkshire Hills Bancorp
Operating segments
Net interest income									8,470,000	25,618,000	15,221,000
Non-interest income									25,230,000	15,414,000	19,678,000
Non-interest expense									2,286,000	2,346,000	3,988,000
Income from continuing operations before income taxes									31,414,000	38,686,000	30,911,000
Income tax expense (benefit)									(2,330,000)	(2,457,000)	(2,277,000)
Net income from continuing operations											33,188,000
Net income									33,744,000	41,143,000	33,188,000
Average assets (in millions)									27,000,000	741,000,000	559,000,000
Eliminations
Operating segments
Net interest income									(12,000,000)	(29,500,000)	(17,000,000)
Non-interest income									(25,230,000)	(15,414,000)	(19,678,000)
Income from continuing operations before income taxes									(37,230,000)	(44,914,000)	(36,678,000)
Net income from continuing operations											(36,678,000)
Net income									(37,230,000)	(44,914,000)	(36,678,000)
Average assets (in millions)									$ (31,000,000)	$ (741,000,000)	$ (392,000,000)