Coal Mining Business (Details) - Disposal Group, Held-for-sale, Not Discontinued Operation - Coal Mining - USD ($)		1 Months Ended	3 Months Ended
	Apr. 06, 2016	Mar. 31, 2016	Mar. 31, 2016
Coal Mining Permits and Related Reclamation Obligations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments for assumption of business		$ 1,800,000
Gain (loss) on disposal of business			$ 1,500,000
Coal Mining Permits and Related Reclamation Obligations | Cost of Products Sold and Operating Expenses
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposal of business		1,500,000
Remaining Coal Mining Assets, Mineral Leases, Real Estate, and a Substantial Portion of Mining Reclamation Obligations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposal of business			(9,200,000)
Impairment charge on write-down			10,700,000
Long-lived assets to be disposed		$ 0	$ 0
Subsequent Event | Remaining Coal Mining Assets, Mineral Leases, Real Estate, and a Substantial Portion of Mining Reclamation Obligations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Payments for assumption of business	$ 10,300,000