Investments - Schedule of Marketable Securities (Details) - USD ($) $ in Millions	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		30.00%
Available-for-sale Securities, Amortized Cost Basis	$ 51.6		$ 41.9
Available-for-sale Securities	51.3		41.6
Platform Science investment	3.5
Zero coupon bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	3.9		3.8
Available-for-sale Securities	3.9		3.9
U.S. treasury and government agencies
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	20.0		6.0
Available-for-sale Securities	19.8		6.0
Asset-backed securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	0.1		0.3
Available-for-sale Securities	0.1		0.3
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	15.1		9.1
Available-for-sale Securities	15.0		9.2
State and municipal bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Amortized Cost Basis	12.5		22.7
Available-for-sale Securities	$ 12.5		$ 22.2

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

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