Investments (Details) - Auction Rate Securities [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 0.4	$ 0.4
Gross Unrealized Gains	4.4	5.4
Gross Unrealized Losses	0.0
Fair Value	4.8	$ 5.8
Par Value Available For Sale Securities	$ 23.4