EMPLOYEE BENEFIT PLAN - Net periodic benefit cost and related components (Details) - Multiple Employers Retirement Income Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 458	$ 483	$ 1,374	$ 1,449
Expected return on plan assets	(710)	(589)	(2,128)	(1,767)
Amortization of net losses	206	213	618	638
Net periodic benefit (credit) cost	$ (46)	$ 107	$ (136)	$ 320