GOODWILL AND OTHER INTANGIBLES - Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Balance at beginning of year	$ 4,935	$ 4,935
Lake Sunapee Bank Group acquisition	95,150	0
Balance at end of year	$ 100,085	$ 4,935