Fair Value Measurements (Details) - Recurring Basis - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fixed-maturity securities available for sale:
Deferred compensation	$ 4.2	$ 3.5
Total assets	43.6	80.3
Liabilities:
Deferred compensation	4.2	3.5
Total liabilities	4.2	3.5
Corporate debt securities
Fixed-maturity securities available for sale:
Securities available for sale	22.5	25.0
Equity securities available for sale
Fixed-maturity securities available for sale:
Securities available for sale	16.9	51.8
Level 1
Fixed-maturity securities available for sale:
Deferred compensation	4.2	3.5
Total assets	21.1	55.3
Liabilities:
Deferred compensation	4.2	3.5
Total liabilities	4.2	3.5
Level 1 \| Corporate debt securities
Fixed-maturity securities available for sale:
Securities available for sale	0.0	0.0
Level 1 \| Equity securities available for sale
Fixed-maturity securities available for sale:
Securities available for sale	16.9	51.8
Level 2
Fixed-maturity securities available for sale:
Deferred compensation	0.0	0.0
Total assets	22.5	25.0
Liabilities:
Deferred compensation	0.0	0.0
Total liabilities	0.0	0.0
Level 2 \| Corporate debt securities
Fixed-maturity securities available for sale:
Securities available for sale	22.5	25.0
Level 2 \| Equity securities available for sale
Fixed-maturity securities available for sale:
Securities available for sale	0.0	0.0
Level 3
Fixed-maturity securities available for sale:
Deferred compensation	0.0	0.0
Total assets	0.0	0.0
Liabilities:
Deferred compensation	0.0	0.0
Total liabilities	0.0	0.0
Level 3 \| Corporate debt securities
Fixed-maturity securities available for sale:
Securities available for sale	0.0	0.0
Level 3 \| Equity securities available for sale
Fixed-maturity securities available for sale:
Securities available for sale	$ 0.0	$ 0.0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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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=75030427&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=82897076&loc=d3e27232-111563

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-Section 45
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