MORTGAGE BANKING AND LOAN SERVICING -Mortgage Servicing Assets and Valuation Allowance - (Details) - Mortgage servicing rights - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Mortgage servicing assets and interest rate locks
Balance at the beginning of the period	$ 7,410	$ 6,120	$ 5,708
Servicing assets capitalized	1,447	1,636	1,525
Servicing rights acquired		1,164
Amortization of servicing assets	(1,352)	(1,510)	(1,313)
Change in valuation allowance	75		200
Balance at the end of the period	7,580	7,410	6,120
Valuation allowance:
Balance at the beginning of the period	200	200	400
Additions expensed		175	25
Reductions credited to operations	(75)	(175)	(225)
Balance at the end of the period	$ 125	$ 200	$ 200