Catastrophe Reinsurance - Catastrophe Reinsurance Premiums (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Liability for Catastrophe Claims [Line Items]
Ceded Catastrophe Reinsurance Premiums	$ 19.0	$ 20.6	$ 26.0
Catastrophe Reinsurance [Member]
Liability for Catastrophe Claims [Line Items]
Ceded Catastrophe Reinsurance Premiums	12.0	12.9	17.7
Property and Casualty Insurance [Member] \| Catastrophe Reinsurance [Member]
Liability for Catastrophe Claims [Line Items]
Ceded Catastrophe Reinsurance Premiums	11.9	12.8	17.6
Life and Health Insurance [Member] \| Catastrophe Reinsurance [Member]
Liability for Catastrophe Claims [Line Items]
Ceded Catastrophe Reinsurance Premiums	$ 0.1	$ 0.1	$ 0.1

Amount of earned premiums ceded to other entities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.1)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-Subparagraph (b),(c)(2)
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6486662&loc=d3e27175-158546

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17)
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

Name:	us-gaap_CededPremiumsEarned
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration