Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant And Equipment [Line Items]

Schedule of property, plant and equipment categories

			2017		2016
Land, surface rights, and mineral rights (1)		$	1,632,003	$	1,643,096
Mining equipment			914,195		915,649
Construction in progress			13,861		11,467
Other equipment			39,626		38,966
Buildings and improvements			72,908		72,998
	Total		2,672,593		2,682,176
Less: accumulated depreciation and depletion			(1,306,838)		(1,249,815)
	Property, plant and equipment, net	$	1,365,755	$	1,432,361

• Includes mineral rights of $366.7million and $685.9 million as of December 31, 2017 and 2016, respectively, attributable to areas where we were not yet engaged in mining operations and, therefore, the mineral rights are not being depleted.

Interest Cost Capitalized

	2017		2016		2015
Interest costs capitalized	$	—	$	1,205	$	1,018

Schedule of future payments on capital equipment lease obligations

2018	$	2,564
2019		1,694
2020		854
2021		28
2022		—
Total		5,140
Less: interest		199
Total principal payments		4,940
Less: current portion		2,435
Capital equipment lease obligations, net of current portion	$	2,505

Leased Equipment [Member]

Property, Plant And Equipment [Line Items]

Schedule of property, plant and equipment categories

			2017		2016
Leased assets		$	13,967	$	13,967
Less: accumulated depreciation and depletion			7,032		4,993
	Capital equipment lease assets, net	$	6,935	$	8,974