Business Segments - Earned Premiums by Product Line (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Life	$ 95.7	$ 94.4
Earned Premiums, Accident and Health	39.1	36.9
Total Earned Premiums	563.4	546.0
Personal Automobile [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	320.7	303.3
Homeowners [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	66.3	68.1
Other Personal Property and Casualty Insurance [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	28.9	29.8
Commercial Automobile [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Earned Premiums, Property and Casualty	$ 12.7	$ 13.5