Investments (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-Sale Securities
Available-for-sale Securities, Amortized Cost Basis	$ 58.8	$ 61.8
Available-for-Sale Securities, Gross Unrealized Gain	0.3	0.0
Available-for-Sale Securities, Gross Unrealized Loss	(0.5)	0.0
Available-for-Sale Securities	58.6	61.8
Current [Member] \| Federal government securities [Member]
Schedule of Available-for-Sale Securities
Available-for-sale Securities, Amortized Cost Basis	5.6
Available-for-Sale Securities, Gross Unrealized Gain	0.0
Available-for-Sale Securities, Gross Unrealized Loss	0.0
Available-for-Sale Securities	5.6
Current [Member] \| U.S. corporate bonds [Member]
Schedule of Available-for-Sale Securities
Available-for-sale Securities, Amortized Cost Basis	3.4	11.2
Available-for-Sale Securities, Gross Unrealized Gain	0.0	0.0
Available-for-Sale Securities, Gross Unrealized Loss	0.0	0.0
Available-for-Sale Securities	3.4	11.2
Noncurrent [Member] \| Marketable equity securities [Member]
Schedule of Available-for-Sale Securities
Available-for-sale Securities, Amortized Cost Basis	6.2	6.2
Available-for-Sale Securities, Gross Unrealized Gain	0.0	0.0
Available-for-Sale Securities, Gross Unrealized Loss	(0.5)	0.0
Available-for-Sale Securities	5.7	6.2
Noncurrent [Member] \| Federal government securities [Member]
Schedule of Available-for-Sale Securities
Available-for-sale Securities, Amortized Cost Basis	28.0	32.0
Available-for-Sale Securities, Gross Unrealized Gain	0.2	0.0
Available-for-Sale Securities, Gross Unrealized Loss	0.0	0.0
Available-for-Sale Securities	28.2	32.0
Noncurrent [Member] \| U.S. corporate bonds [Member]
Schedule of Available-for-Sale Securities
Available-for-sale Securities, Amortized Cost Basis	15.6	12.4
Available-for-Sale Securities, Gross Unrealized Gain	0.1	0.0
Available-for-Sale Securities, Gross Unrealized Loss	0.0	0.0
Available-for-Sale Securities	15.7	12.4
Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-Sale Securities
Available-for-Sale Securities	$ 58.6	$ 61.8

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 320
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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