EMPLOYEE BENEFIT PLAN - Net periodic benefit cost and related components (Details) (Multiple Employer Retirement Income Plan, USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Multiple Employer Retirement Income Plan
Multiemployer Plans [Line Item]
Service cost
Interest cost	436	467	870	934
Expected return on plan assets	(511)	(462)	(1,022)	(924)
Amortization of net losses	196	167	391	334
Net periodic benefit cost	$ 121	$ 172	$ 239	$ 344