SIGNIFICANT ACCOUNTING POLICIES - Benefits and Investment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($)
SIGNIFICANT ACCOUNTING POLICIES
Premium paid for split dollar life insurance agreements	$ 0	$ 0	$ 0
Agreements terminated | item	0	0
Amount received on termination of certain split dollar agreements			$ 7,591