ASSET RETIREMENT OBLIGATIONS (Tables)

12 Months Ended

Dec. 31, 2015

ASSET RETIREMENT OBLIGATIONS

Schedule of estimated payments of asset retirement obligations

Year Ending December 31,	(in thousands)
2016	$	1,251
2017	1,073
2018	4,582
2019	4,832
2020	5,093
Thereafter	211,654
Aggregate undiscounted asset retirement obligations	228,485
Effect of discounting	(104,800)
Total asset retirement obligations	123,685
Less: current portion	(1,251)
Asset retirement obligations	$	122,434

Schedule of activity affecting the asset retirement and mine closing liability

	Year ended December 31,
	2015		2014
	(in thousands)
Beginning balance	$	93,140	$	82,898
Accretion expense	3,192		2,730
Payments	(519)		(1,134)
Assumption of existing liability	31,372		6,042
Disposition	—		(5,246)
Allocation of liability associated with acquisitions, mine development and change in assumptions	(3,500)		7,850
Ending balance	$	123,685	$	93,140