Fair Value Measurements - Financial Instruments at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Measured at fair value on a recurring basis: | Level 1
Assets:
Investment securities	$ 8.1	$ 17.0
Foreign currency forward contracts	0.0	0.0
Funds associated with Israeli severance liability	0.0	0.0
Royalty Pharma contingent milestone payments	0.0	0.0
Total assets	8.1	17.0
Liabilities:
Foreign currency forward contracts	0.0	0.0
Contingent consideration	0.0	0.0
Total liabilities	0.0	0.0
Measured at fair value on a recurring basis: | Level 2
Assets:
Investment securities	0.0	0.0
Foreign currency forward contracts	2.7	6.3
Funds associated with Israeli severance liability	14.2	16.3
Royalty Pharma contingent milestone payments	0.0	0.0
Total assets	16.9	22.6
Liabilities:
Foreign currency forward contracts	9.1	3.8
Contingent consideration	0.0	0.0
Total liabilities	9.1	3.8
Measured at fair value on a recurring basis: | Level 3
Assets:
Investment securities	0.0	0.0
Foreign currency forward contracts	0.0	0.0
Funds associated with Israeli severance liability	0.0	0.0
Royalty Pharma contingent milestone payments	125.5	134.5
Total assets	125.5	134.5
Liabilities:
Foreign currency forward contracts	0.0	0.0
Contingent consideration	16.2	22.0
Total liabilities	16.2	22.0
Measured at fair value on a non-recurring basis: | Level 1
Liabilities:
Definite-lived intangible assets	0.0	0.0
Measured at fair value on a non-recurring basis: | Level 2
Liabilities:
Definite-lived intangible assets	0.0	0.0
Measured at fair value on a non-recurring basis: | Level 3
Liabilities:
Definite-lived intangible assets	$ 0.0	$ 11.5