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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 483	$ 502	$ 1,449	$ 1,505
Expected return on plan assets	(589)	(533)	(1,767)	(1,599)
Amortization of net losses	213	200	638	599
Net periodic benefit cost	$ 107	$ 169	$ 320	$ 505