Acquisition-Related Obligations - Narrative (Details) - USD ($)	3 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Nov. 09, 2018	Jul. 12, 2016
Business Acquisition, Contingent Consideration [Line Items]
Liabilities held for sale			$ 39,867,000	$ 79,898,000
Acquisition related obligations, current			19,099,000	33,639,000
Discount			1,491,000	4,834,000
Contingent Revenue Obligation, Threshold One
Business Acquisition, Contingent Consideration [Line Items]
Percentage of revenue					1.50%
Revenue threshold					$ 500,000,000
Contingent Revenue Obligation, Threshold Two
Business Acquisition, Contingent Consideration [Line Items]
Percentage of revenue					1.00%
Revenue threshold					$ 500,000,000
Contingent Revenue Obligation
Business Acquisition, Contingent Consideration [Line Items]
Liabilities held for sale			28,967,000	52,427,000
Acquisition related obligations, current			11,393,000	14,646,000
Payment of contingent revenue obligation	$ 15,084,000	$ 9,627,000
Unclaimed unsecured claims	$ 374,000
Payments due			28,967,000	52,427,000
Environmental Settlement Obligations
Business Acquisition, Contingent Consideration [Line Items]
Liabilities held for sale			9,237,000	13,594,000
Acquisition related obligations, current			6,044,000	6,185,000
Discount			1,154,000	2,711,000
Payments due			10,391,000	16,305,000
Reclamation Funding Liability
Business Acquisition, Contingent Consideration [Line Items]
Acquisition related obligations, current				10,808,000
Discount				1,192,000
Payments due			0	$ 12,000,000		$ 50,000,000
Payments due immediately						8,000,000
Payments due 2017						10,000,000
Payments due 2018						10,000,000
Payments due 2019						10,000,000
Payments due 2020						$ 12,000,000
Remaining payments			$ 0