Investments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Investments in available-for-sale securities
Amortized Cost	$ 67.2	$ 65.7
Gross Unrealized Gains	0.1	1.4
Gross Unrealized Losses	(1.8)	(0.1)
Current [Member] | Federal government securities [Member]
Investments in available-for-sale securities
Amortized Cost	2.8	2.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	2.8	2.8
Current [Member] | U.S. corporate bonds [Member]
Investments in available-for-sale securities
Amortized Cost	10.6	2.4
Gross Unrealized Gains	0.1	0
Gross Unrealized Losses	0	0
Fair Value	10.7	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	(1.7)	0
Fair Value	9.2	12.2
Noncurrent [Member] | Federal government securities [Member]
Investments in available-for-sale securities
Amortized Cost	28.8	28.8
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(0.1)	(0.1)
Fair Value	28.7	28.7
Noncurrent [Member] | U.S. corporate bonds [Member]
Investments in available-for-sale securities
Amortized Cost	14.1	20.8
Gross Unrealized Gains	0	0.1
Gross Unrealized Losses	0	0
Fair Value	14.1	20.9
Fair Value, Measurements, Recurring [Member]
Investments in available-for-sale securities
Fair Value	$ 65.5	$ 67.0