Debt and Credit Arrangements - Interest Expense and Financing Cost Amortization (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Debt Instrument
Interest expense excluding amortization	$ 2.2	$ 7.6	$ 4.2	$ 14.8
Financing costs amortization	1.1	1.1	2.3	2.1
Revolving Credit Facility
Debt Instrument
Interest expense excluding amortization	1.8	4.6	3.1	9.4
Financing costs amortization	0.8	0.9	1.8	1.7
Revolving Credit Facility | Term loan
Debt Instrument
Interest expense excluding amortization	0.5	4.0	1.1	8.2
Revolving Credit Facility | Senior secured revolving credit facility
Debt Instrument
Interest expense excluding amortization	$ 1.3	$ 0.6	$ 2.0	$ 1.2