INCOME TAXES - Open Tax Year (Details)	12 Months Ended
	Dec. 31, 2018
Federal
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2018
Connecticut | Minimum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2015
Connecticut | Maximum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2018
Massachusetts | Minimum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2015
Massachusetts | Maximum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2018
New Hampshire | Minimum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2016
New Hampshire | Maximum
Income Tax Contingency [Line Items]
Open tax years that remain subject to examination	2018