Litigation, Commitments and Contingencies - Capital Lease (Details) $ in Millions	Dec. 31, 2017 USD ($) lease
Loss Contingency Information About Litigation Matters
Contingent lease liability, number of domestic leases | lease	49
Estimated maximum amount of undiscounted payments for contingent lease liabilities	$ 4.4
Capital lease related to Industrial Revenue Bonds
Loss Contingency Information About Litigation Matters
Investments in Industrial Revenue Bonds	$ 80.2
Investments in Industrial Revenue Bonds, percent owned	100.00%