Cash, Cash Equivalents and Marketable Securities Available-for-Sale (Duration Periods) (Details) $ in Millions	Mar. 31, 2016 USD ($)
Amortized Cost
Duration of one year or less	$ 38.1
Duration of one through three years	287.7
Duration of three through five years	10.3
Total	336.1
Fair Value
Duration of one year or less	38.0
Duration of one through three years	288.4
Duration of three through five years	10.4
Total	$ 336.8