Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Accrued benefits	$ 21.7	$ 21.2
Current portion of postretirement benefit obligation	2.9	3.0
Other taxes payable	9.9	9.1
Current portion of black lung liability	4.6	4.5
Other	7.9	7.8
Total accrued liabilities	$ 47.0	$ 45.6