Investments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items]
Available for sale investments	$ 51.2	$ 58.4
Payments to acquire available-for-sale securities	16.6	20.9	$ 20.0
Unrealized gain (loss) on investments, net of taxes of $0.4, ($0.2) and $0.1	(1.4)	0.6	$ (1.2)
Municipal Bonds
Debt Securities, Available-for-sale [Line Items]
Available for sale investments	49.0	54.2
Unobservable inputs for which little or no market data exists (Level 3)
Debt Securities, Available-for-sale [Line Items]
Available for sale investments	2.3	4.1
Payments to acquire available-for-sale securities	$ 5.0	$ 5.0

Amount 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 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Paragraph 2
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Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

+ References

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-Publisher FASB
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-SubTopic 10
-Section 45
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Amount of cash outflow to acquire investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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