ASSET RETIREMENT OBLIGATIONS (Tables)

12 Months Ended

Dec. 31, 2016

ASSET RETIREMENT OBLIGATIONS

Schedule of activity affecting the asset retirement and mine closing liability

	Year Ended December 31,
	2016		2015
	(in thousands)
Beginning balance	$	123,685	$	93,140
Accretion expense		3,769		3,192
Payments		(379)		(519)
Assumption of existing liability		—		31,372
Allocation of liability associated with acquisitions, mine development and change in assumptions		(1,374)		(3,500)
Ending balance	$	125,701	$	123,685

Schedule of estimated payments of asset retirement obligations

Year Ended
December 31,	(in thousands)
2017	$	435
2018		385
2019		158
2020		147
2021		80
Thereafter		235,237
Aggregate undiscounted asset retirement obligations		236,442
Effect of discounting		(110,741)
Total asset retirement obligations		125,701
Less: current portion		(435)
Asset retirement obligations	$	125,266