ASSET RETIREMENT OBLIGATIONS (Tables)

12 Months Ended

Dec. 31, 2017

ASSET RETIREMENT OBLIGATIONS

Schedule of activity affecting the asset retirement and mine closing liability

	Year Ended December 31,
	2017		2016
	(in thousands)
Beginning balance	$	125,701	$	123,685
Accretion expense		3,793		3,769
Payments		(1,046)		(379)
Allocation of liability associated with acquisitions, mine development and change in assumptions		2,152		(1,374)
Ending balance	$	130,600	$	125,701

Schedule of estimated payments of asset retirement obligations

Year Ended
December 31,	(in thousands)
2018	$	3,850
2019		454
2020		433
2021		—
2022		1,256
Thereafter		238,604
Aggregate undiscounted asset retirement obligations		244,597
Effect of discounting		(113,997)
Total asset retirement obligations		130,600
Less: current portion		(3,850)
Asset retirement obligations	$	126,750