EMPLOYEE RETIREMENT PLANS - Information Relating to the Company's Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Change in benefit obligation:
Benefit obligation, beginning of year	$ 27,563	$ 22,594
Service cost	1,214	1,415
Interest cost	1,013	875
Actuarial loss	2,952	2,679
Plan amendment	434
Benefit obligation, end of year	33,176	27,563
Unfunded status of the plan, end of year	33,176	27,563
Noncurrent liability	$ 33,176	$ 27,563