Condensed Consolidated Statements of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Earned premiums (ceded to affiliates $215.2 and $215.2 for the three months ended, respectively, and $647.4 and $639.0 for the nine months ended, respectively)	$ 270.2	$ 266.0	$ 801.0	$ 790.8
Net investment income (affiliate $1.3 and $1.3 for the three months ended, respectively, and $3.7 and $3.7 for the nine months ended, respectively)	18.9	18.8	57.0	55.4
Net realized gains on investments:
Total other-than-temporary impairment losses	(1.1)	(0.3)	(2.3)	(2.6)
Portion of loss recognized in other comprehensive income	0	0	0	0
Other net realized investment gains	2.7	7.8	19.9	18.3
Total net realized gains on investments	1.6	7.5	17.6	15.7
Other income from affiliates	0.6	0.4	1.4	1.4
Total revenues	291.3	292.7	877.0	863.3
Losses and loss expenses (ceded to affiliates $131.6 and $137.9 for the three months ended, respectively, and $417.3 and $434.0 for the nine months ended, respectively)	184.4	178.8	546.6	537.9
Acquisition and operating expenses	91.4	90.9	277.2	266.7
Interest expense (affiliates $0.2 and $0.1 for the three months ended, respectively, and $0.5 and $0.5 for the nine months ended, respectively)	1.4	1.6	4.0	7.1
Other expenses	1.0	2.7	5.3	6.6
Total expenses	278.2	274.0	833.1	818.3
Income before federal income taxes	13.1	18.7	43.9	45.0
Federal income tax expense	1.2	0.2	1.9	0.6
Net income	$ 11.9	$ 18.5	$ 42.0	$ 44.4
Earnings per common share:
Basic (usd per share)	$ 0.29	$ 0.46	$ 1.03	$ 1.09
Diluted (usd per share)	$ 0.28	$ 0.45	$ 1.02	$ 1.09
Dividends paid per common share (usd per share)	$ 0.10	$ 0.10	$ 0.30	$ 0.30