Fair Value Measurement - Contingent Liability Rollforward (Details) - Level 3 - Contingent acquisition consideration - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the beginning and ending balances for the liabilities measured at fair value using significant unobservable inputs (Level 3)
Balance at the beginning of the period	$ 0.0	$ 0.0	$ (0.3)
Increase related to new acquisitions	0.0	0.0	0.0
Payment of contingent consideration	0.0	0.0	0.1
Change in fair value	0.0	0.0	0.2
Balance at the end of the period	$ 0.0	$ 0.0	$ 0.0