Segment Information - Reconciliation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 180,064	$ 287,506	$ 570,484	$ 1,063,408
Segment Reconciling Items
Segment Reporting Information [Line Items]
Total revenues	4,835	6,665	14,875	25,458
Mining | Operating Segments
Segment Reporting Information [Line Items]
Total revenues	$ 175,229	$ 280,841	$ 555,610	$ 1,037,950