Securities Sold Under Agreements to Repurchase and Other Short-Term Debt (Information Regarding Other Borrowed Funds) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Short-term Debt [Line Items]
Amount outstanding at year end	$ 258,464	$ 250,314
FHLBB Short Term Borrowings [Member]
Short-term Debt [Line Items]
Amount outstanding at year end	0	0	0
Maximum amount outstanding during the year	18,900	72,500	97,000
Average amount outstanding during the year	212	17,259	38,290
Weighted average-rate during the year	0.31%	0.30%	0.28%
Weighted average rate at year-end	0.00%	0.00%	0.00%
Securities Sold under Agreement to Repurchase - Short-Term [Member]
Short-term Debt [Line Items]
Amount outstanding at year end	258,464	250,314	287,520
Maximum amount outstanding during the year	292,692	284,297	303,420
Average amount outstanding during the year	$ 192,868	$ 212,644	$ 230,281
Weighted average-rate during the year	0.18%	0.41%	0.73%
Weighted average rate at year-end	0.26%	0.18%	0.47%