EMPLOYEE BENEFIT PLAN - Net periodic benefit cost and related components (Details) (Multiple Employers Retirement Income Plan, USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Multiple Employers Retirement Income Plan
Multiemployer Plans [Line Item]
Interest cost	$ 474	$ 486
Expected return on plan assets	(565)	(560)
Amortization of net losses	198	133
Net periodic benefit cost	$ 107	$ 59