Borrowings (Certain Information of Federal Home Loan Bank of Boston Advances) (Details) (Federal Home Loan Bank of Boston [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Federal Home Loan Bank of Boston [Member]
Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items]
Average amount outstanding during the period	$ 70,693	$ 13,901	$ 61,936
Amount outstanding at end of period	200,000	0	40,500
Highest month end balance during period	$ 200,000	$ 60,000	$ 102,929
Weighted-average interest rate at end of period	0.37%	0.00%	0.28%
Weighted-average interest rate during the period	0.35%	0.30%	0.27%