MORTGAGE SERVICING RIGHTS - Balance of loans serviced for others and fair value of mortgage servicing rights (Details) - Balance of loans serviced for others and fair value of mortgage servicing rights - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Residential mortgage loans serviced for others	$ 120,429	$ 125,243
Fair value of mortgage servicing rights	$ 1,004	$ 902