Commitments and Contingencies - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Total rent expense	$ 2,300,000	$ 3,200,000	$ 4,000,000
Promissory notes as security for letters of credit	76,700,000	$ 76,000,000
Pending Litigation Royalty, Transportation and Related Costs
Loss Contingencies [Line Items]
Estimated compensation which would be payable if interpretation is correct	56,300,000
Amount accrued for improbable loss	$ 0