Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - Fair Value Measured On A Recurring Basis - USD ($) $ in Millions		Mar. 31, 2018		Dec. 31, 2017
Financial Assets
Cash equivalents		$ 33.3		$ 40.4
Investments in marketable securities	[1]	81.0		77.8
Foreign currency forward contracts		1.2	[2]	0.2	[1]
Financial Liabilities
Contingent payment arrangements	[2]	9.8		9.4
Affiliate equity obligations	[2]	79.4		49.2
Foreign currency forward contracts	[2]	1.3		0.6
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets
Cash equivalents		33.3		40.4
Investments in marketable securities	[1]	81.0		77.8
Foreign currency forward contracts		0.0	[2]	0.0	[1]
Financial Liabilities
Contingent payment arrangements	[2]	0.0		0.0
Affiliate equity obligations	[2]	0.0		0.0
Foreign currency forward contracts	[2]	0.0		0.0
Significant Other Observable Inputs (Level 2)
Financial Assets
Cash equivalents		0.0		0.0
Investments in marketable securities	[1]	0.0		0.0
Foreign currency forward contracts		1.2	[2]	0.2	[1]
Financial Liabilities
Contingent payment arrangements	[2]	0.0		0.0
Affiliate equity obligations	[2]	0.0		0.0
Foreign currency forward contracts	[2]	1.3		0.6
Significant Unobservable Inputs (Level 3)
Financial Assets
Cash equivalents		0.0		0.0
Investments in marketable securities	[1]	0.0		0.0
Foreign currency forward contracts		0.0	[2]	0.0	[1]
Financial Liabilities
Contingent payment arrangements	[2]	9.8		9.4
Affiliate equity obligations	[2]	79.4		49.2
Foreign currency forward contracts	[2]	$ 0.0		$ 0.0

[1] Amounts are presented within Investments and other assets.

[2] Amounts are presented within Other liabilities.