Accounts Payable and Accrued Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Trade payables	$ 3.9	$ 6.3
Compensation and benefits payable	21.0	17.4
Postretirement health and life benefit obligations - current	15.4	14.7
Accrued severance payments	4.1	3.9
Accrued lease turnover - current	1.6	1.8
Accrued interest payable on debt	0.6	0.2
Other accrued liabilities	5.8	3.9
Accounts payable and accrued liabilities	$ 52.4	$ 48.2