PENSION PLAN - Plan Assets at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	$ 5,166	$ 4,573	$ 4,486
Level I
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	4,494	4,161
Level III
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	672	412
Cash
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	465	732
Cash | Level I
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	465	732
Fixed income
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	1,188	1,280
Fixed income | Level I
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	1,188	1,280
Alternative investments
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	672	412
Alternative investments | Level III
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	672	412
Domestic equities
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	1,653	1,280
Domestic equities | Level I
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	1,653	1,280
Foreign equities
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	1,188	869
Foreign equities | Level I
Plan's assets at fair value by level, within the fair value hierarchy
Total assets at fair value	$ 1,188	$ 869