Commitments and Contingencies - Narrative (Details)	1 Months Ended	12 Months Ended
	May 31, 2017 USD ($)	Dec. 31, 2017 USD ($) lawsuit	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Automobile and workers’ compensation claims		$ 500,000
Number of claims alleging subsidence caused by oil and gas production | lawsuit		1
Accrued future legal costs		$ 0	$ 500,000
Release of accrual for future legal costs	$ 500,000
Parental guaranteed obligations		$ 48,200,000
Minimum [Member]
Loss Contingencies [Line Items]
Operating lease term		1 year
Aggregate medical claims for umbrella insurance coverage per calendar year		$ 4,500,000
Maximum [Member]
Loss Contingencies [Line Items]
Operating lease term		8 years