Mergers and Acquisition Activity (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Latremore's Insurance Agency [Member]
Business Acquisition [Line Items]
Acquisition of intangible assets	$ 2.1
Acquisition of goodwill	1.3
Acquisition of fixed assets	0.1
Purchase price of intangible asset and goodwill	3.5
Legacy Bank [Member]
Business Acquisition [Line Items]
Acquisition of intangible assets	1.3
Acquisition of goodwill	12.5
Purchase price of intangible asset and goodwill	8.9
Number of bank branches converted to the Company	4
Acquisition of loans	39.9
Acquisition of deposits	144.8
Acquisition of other assets	$ 2.8
Berkshire Hills Bancorp and Legacy Banks [Member]
Business Acquisition [Line Items]
Number of bank branches converted to the Company	3
Number of bank branches deposits and loans converted to the Company	1