CONDENSED FINANCIAL STATEMENTS OF PARENT COMPANY (Details 3) (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
Cash flows from operating activities:
Net income	$ 11,398	$ 11,988	$ 11,464	$ (1,106)	$ 10,537	$ 8,104	$ 12,037	$ 10,465	$ 33,744	$ 41,143	$ 33,188
Adjustments to reconcile net income to net cash (used) provided by operating activities:
Other, net									(135)	22,404	19,604
Net cash provided by operating activities									55,823	127,411	28,654
Cash flows from investing activities:
Acquisitions, net of cash paid									423,416		(111,328)
other, net									(5,384)		(565)
Net cash used in investing activities									(369,304)	(515,194)	(255,523)
Cash flows from financing activities:
Proceed from issuance of long term debt											74,138
Net proceeds from reissuance of treasury stock									(2,467)	(12,249)
Payment to repurchase common stock											3,044
Common stock cash dividends paid									(18,075)	(18,118)	(15,634)
Net cash provided by financing activities									309,696	365,078	249,331
Net change in cash and cash equivalents									(3,785)	(22,705)	22,462
Cash and cash equivalents at beginning of year				75,539					75,539
Cash and cash equivalents at end of year	71,754				75,539				71,754	75,539
Reportable legal entity | Berkshire Hills Bancorp
Cash flows from operating activities:
Net income									33,744	41,143	33,188
Adjustments to reconcile net income to net cash (used) provided by operating activities:
Equity in undistributed income of subsidiaries									(25,230)	(15,414)	(19,678)
Other, net									3,247	763	1,897
Net cash provided by operating activities									11,761	26,492	15,407
Cash flows from investing activities:
Acquisitions, net of cash paid											(64,230)
Purchase of securities										(770)
other, net										588	1,000
Net cash used in investing activities										(182)	(63,230)
Cash flows from financing activities:
Proceed from issuance of short term debt											10,000
Proceed from issuance of long term debt											74,153
Net proceeds from common stock										3,045
Net proceeds from reissuance of treasury stock									1,064		3,044
Payment to repurchase common stock									(2,468)	(12,249)
Common stock cash dividends paid									(18,075)	(18,118)	(15,634)
Other, net									(1,903)	1,513
Net cash provided by financing activities									(21,382)	(25,809)	71,563
Net change in cash and cash equivalents									(9,621)	501	23,740
Cash and cash equivalents at beginning of year				40,154				39,653	40,154	39,653	15,913
Cash and cash equivalents at end of year	$ 30,533				$ 40,154				$ 30,533	$ 40,154	$ 39,653