Commitments and Contingencies - Operating and Capital Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Future minimum payments under operating leases
2018	$ 20.8
2019	18.8
2020	14.3
2021	10.9
2022	9.1
2023 and beyond	9.9
Future minimum rentals to be received under operating subleases
2018	0.3
2019	0.1
Rent expense	19.0	$ 16.2	$ 15.2
Future minimum payments under capital leases net of leasehold improvement allowances
2018	4.9
2019	3.1
2020	3.6
2021	3.6
2022	3.7
2023 and beyond	7.6
Capital lease obligations imputed interest	$ 3.6