SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE AND OTHER SHORT-TERM DEBT (Information Regarding Other Borrowed Funds) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Short-term Debt [Line Items]
Amount outstanding at year end	$ 286,639	$ 258,464
FHLBB Short Term Borrowings [Member]
Short-term Debt [Line Items]
Maximum amount outstanding during the year	63,000	18,900	$ 72,500
Average amount outstanding during the year	$ 3,953	$ 212	$ 17,259
Weighted average-rate during the year	0.33%	0.31%	0.30%
Securities Sold under Agreement to Repurchase - Short-Term [Member]
Short-term Debt [Line Items]
Amount outstanding at year end	$ 286,639	$ 258,464	$ 250,314
Maximum amount outstanding during the year	318,788	292,692	284,297
Average amount outstanding during the year	$ 226,913	$ 192,868	$ 212,644
Weighted average-rate during the year	0.22%	0.18%	0.41%
Weighted average rate at year-end	0.19%	0.26%	0.18%