Investments - Contractual Maturity (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Investments [Abstract]
Amortized Cost Due within 1 year	$ 12.2
Amortized Cost After 1 year but within 5 years	32.5
Amortized Cost After 5 years but within 10 years	7.2
Amortized Cost Due after 10 years	0.0
Available-for-sale securities, amortized cost	51.9	$ 42.5
Fair Value Due within 1 year	12.2
Fair Value After 1 year but within 5 years	32.5
Fair Value After 5 years but within 10 years	7.3
Fair Value Due after 10 years	0.0
Available for Sale	$ 52.0	$ 43.0