CLOSURE AND POST-CLOSURE LIABILITIES (Anticipated Payments) (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Environmental Property Sale, Disposal or Abandonment Costs
2016	$ 8,160
2017	9,061
2018	9,001
2019	7,621
2020	3,442
Thereafter	262,365
Undiscounted closure and post-closure liabilities	299,650
Less: Discount at credit-adjusted risk-free rate	(156,145)
Less: Undiscounted estimated closure and post-closure liabilities relating to airspace not yet consumed	(87,256)
Present value of closure and post-closure liabilities	$ 56,249	$ 50,701	$ 47,085