EMPLOYEE BENEFIT PLAN - Net periodic benefit cost and related components (Details) - Multiple Employers Retirement Income Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 458	$ 483	$ 916	$ 966
Expected return on plan assets	(709)	(589)	(1,418)	(1,178)
Amortization of net losses	206	213	412	425
Net periodic benefit (credit) cost	$ (45)	$ 107	$ (90)	$ 213