Commitments and Contingencies - Retirement Plans (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) employee	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Number of participants | employee	1,100
Corrpro
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Benefit obligation	$ 7.1	$ 7.5
Fair value of plan assets	$ 7.9	9.3
Assumptions used calculating benefit obligation, discount rate	2.80%
Amounts for asset (liability) recognized in statement of financial position	$ 0.8
United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution plan cost	5.7	6.3	$ 5.5
Foreign
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution plan cost	$ 1.1	$ 1.0	$ 0.8