Financial Instruments - Leases (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Future minimum lease payments under capital leases
2018	$ 1.4
2019	1.3
2020	1.2
2021	0.2
Total	4.1
Less amount representing interest (at rates ranging from 4.3% to 7.0%)	0.3
Present value of net minimum capital lease payments	3.8
Less current installments of obligations under capital leases	1.3
Obligations under capital leases, excluding current installments	2.5
Future minimum lease payments under operating leases
2018	11.4
2019	9.5
2020	7.5
2021	3.5
2022	1.8
Thereafter	3.2
Total	$ 36.9
Minimum
Capital Leases
Interest rate for capital leases (as a percent)	4.30%
Maximum
Capital Leases
Interest rate for capital leases (as a percent)	7.00%