Condensed Consolidated Statements of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Statement [Abstract]
Earned premiums (ceded to affiliates $216.8 and $213.1 for the three months ended, respectively, and $432.2 and $423.8 for the six months ended, respectively)	$ 268.3	$ 263.5	$ 530.8	$ 524.8
Net investment income (affiliate $1.2 and $1.2 for the three months ended, respectively, and $2.4 and $2.4 for the six months ended, respectively)	20.5	19.7	38.1	36.6
Net realized gains on investments:
Total other-than-temporary impairment losses	(0.3)	(2.0)	(1.2)	(2.3)
Portion of loss recognized in other comprehensive income	0	0	0	0
Other net realized investment gains	5.6	3.5	17.2	10.5
Total net realized gains on investments	5.3	1.5	16.0	8.2
Other income from affiliates	0.3	0.6	0.8	1.0
Total revenues	294.4	285.3	585.7	570.6
Losses and loss expenses (ceded to affiliates $143.5 and $164.4 for the three months ended, respectively, and $285.7 and $296.2 for the six months ended, respectively)	190.4	186.1	362.2	359.1
Acquisition and operating expenses	97.3	87.0	185.8	175.8
Interest expense (affiliates $0.1 and $0.2 for the three months ended, respectively, and $0.3 and $0.4 for the six months ended, respectively)	1.3	3.8	2.6	5.5
Other expenses	2.3	2.1	4.3	3.9
Total expenses	291.3	279.0	554.9	544.3
Income before federal income taxes	3.1	6.3	30.8	26.3
Federal income tax expense	0.1	0.1	0.7	0.4
Net income	$ 3.0	$ 6.2	$ 30.1	$ 25.9
Earnings per common share:
Basic (usd per share)	$ 0.07	$ 0.15	$ 0.74	$ 0.64
Diluted (usd per share)	$ 0.07	$ 0.15	$ 0.73	$ 0.64
Dividends paid per common share (usd per share)	$ 0.10	$ 0.10	$ 0.20	$ 0.20