CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY (Details 2) (USD $) In Thousands, unless otherwise specified	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	Dec. 31, 2013	Dec. 31, 2012
Income:
Total net revenue	$ 60,847	$ 59,590	$ 58,835	$ 47,189	$ 55,556	$ 57,983	$ 56,710	$ 56,735	$ 226,461	$ 226,984	$ 197,444
Interest expense	7,369	7,107	6,846	7,029	8,817	8,635	8,593	8,944	28,351	34,989	32,551
Income tax expense (benefit)	3,875	4,230	4,119	(461)	4,762	3,917	4,038	4,387	11,763	17,104	13,223
Net income	11,398	11,988	11,464	(1,106)	10,537	8,104	12,037	10,465	33,744	41,143	33,188
Reportable legal entity | Berkshire Hills Bancorp
Income:
Dividends from subsidiaries									12,000	29,500	17,000
Other									2,317	2,317	481
Total net revenue									14,317	31,817	17,481
Interest expense									5,847	6,199	2,260
Operating expenses									2,286	2,346	3,988
Total expense									8,133	8,545	6,248
Income before income taxes and equity in undistributed income of subsidiaries									6,184	23,272	11,233
Income tax expense (benefit)									(2,330)	(2,457)	(2,277)
Income before equity in undistributed income of subsidiaries									8,514	25,729	13,510
Equity in undistributed income (loss) of subsidiaries									25,230	15,414	19,678
Net income									$ 33,744	$ 41,143	$ 33,188