Fair Value Accounting - Assets and liabilities measured at fair value on recurring basis (Details) - USD ($) $ in Millions		Mar. 31, 2020		Dec. 31, 2019
Liabilities:
Derivative liability		$ 8.4
Fair Value, Measurements, Recurring
Assets:
Cash equivalents		135.0		$ 155.3
Total assets		135.0		155.3
Liabilities:
Contingent consideration liability		4.2	[1]	6.4
Total liabilities		12.6		10.7
Fair Value, Measurements, Recurring | Interest Rate Swap
Liabilities:
Derivative liability	[2]	8.4		4.3
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Assets:
Cash equivalents		135.0		155.3
Total assets		135.0		155.3
Liabilities:
Contingent consideration liability		0.0	[1]	0.0
Total liabilities		0.0		0.0
Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring | Interest Rate Swap
Liabilities:
Derivative liability	[2]	0.0		0.0
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Assets:
Cash equivalents		0.0		0.0
Total assets		0.0		0.0
Liabilities:
Contingent consideration liability		0.0	[1]	0.0
Total liabilities		8.4		4.3
Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring | Interest Rate Swap
Liabilities:
Derivative liability	[2]	8.4		4.3
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Assets:
Cash equivalents		0.0		0.0
Total assets		0.0		0.0
Liabilities:
Contingent consideration liability		4.2	[1]	6.4
Total liabilities		4.2		6.4
Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring | Interest Rate Swap
Liabilities:
Derivative liability	[2]	$ 0.0		$ 0.0

[1] Current portion included in accrued liabilities and non-current portion included in other liabilities on the Consolidated Balance Sheets.

[2] Included in other liabilities on the Consolidated Balance Sheets.