Investments (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Investments in available-for-sale securities
Amortized Cost	$ 63.4	$ 65.7
Gross Unrealized Gains	0	1.4
Gross Unrealized Losses	(1.4)	(0.1)
Current [Member] | Federal government securities [Member]
Investments in available-for-sale securities
Amortized Cost		2.8
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		2.8
Current [Member] | U.S. corporate bonds [Member]
Investments in available-for-sale securities
Amortized Cost	10.9	2.4
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	10.9	2.4
Noncurrent [Member] | Marketable equity securities [Member]
Investments in available-for-sale securities
Amortized Cost	10.9	10.9
Gross Unrealized Gains	0	1.3
Gross Unrealized Losses	(1.4)	0
Fair Value	9.5	12.2
Noncurrent [Member] | Federal government securities [Member]
Investments in available-for-sale securities
Amortized Cost	29.4	28.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(0.1)
Fair Value	29.4	28.7
Noncurrent [Member] | U.S. corporate bonds [Member]
Investments in available-for-sale securities
Amortized Cost	12.2	20.8
Gross Unrealized Gains	0	0.1
Gross Unrealized Losses	0	0
Fair Value	12.2	20.9
Fair Value, Measurements, Recurring [Member]
Investments in available-for-sale securities
Fair Value	$ 62.0	$ 67.0