Condensed Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Earned premiums (affiliated net assumed $114.8 and $113.4, respectively)	$ 317.3	$ 319.9
Net investment income (affiliate $1.2 and $1.2, respectively)	18.7	17.4
Net realized gains on investments:
Total other-than-temporary impairment losses	(2.1)	(3.7)
Other net realized investment gains	9.9	5.0
Total net realized gains on investments	7.8	1.3
Other income from affiliates	0.5	0.6
Total revenues	344.3	339.2
Losses and loss expenses (affiliated net assumed $86.2 and $93.7, respectively)	234.0	225.0
Acquisition and operating expenses (affiliated net assumed $80.3 and $70.6, respectively)	112.2	107.5
Interest expense (affiliates $0.2 and $0.2, respectively)	1.4	1.3
Other expenses	1.9	1.6
Costs and Expenses	349.5	335.4
Income before federal income taxes	(5.2)	3.8
Current Income Tax Expense (Benefit)	(0.1)	0.0
Deferred Income Tax Expense (Benefit)	(1.0)	0.8
Federal income tax expense	(1.1)	0.8
Net income	$ (4.1)	$ 3.0
(Loss) earnings per common share:
Basic (usd per share)	$ (0.10)	$ 0.07
Diluted (usd per share)	(0.10)	0.07
Dividends paid per common share (usd per share)	$ 0.10	$ 0.10