OFF-BALANCE SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES - Leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Noncancelable future operating lease commitments
2018	$ 2,033
2019	1,610
2020	1,237
2021	1,099
2022	817
Thereafter	2,911
Total	9,707
Rent expense under noncancelable operating lease obligations, net of income from noncancelable subleases	$ 2,300	$ 2,300	$ 1,900