Liabilities - Other Liabilities (Details) - USD ($) $ in Millions	39 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Other liabilities
Contributions to deferred compensation plan	$ 0.0
Other Assets
Other liabilities
Deferred compensation plan assets	2.1	$ 2.7
Other Liabilities
Other liabilities
Deferred compensation plan liabilities	2.2	3.1
Medical and dental benefits	2.0	2.0
Asset retirement obligations	3.2	3.2
Income taxes payable	1.4	$ 1.0
Accrued and deferred deposit payments	$ 1.4