Condensed Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets
Fixed maturities, available-for-sale, at fair value (amortized cost $1,894.0 and $1,831.3, respectively)	$ 1,964.0	$ 1,891.9
Equity securities, available-for-sale, at fair value (cost $236.7 and $235.5, respectively)	310.6	310.4
Other invested assets, available-for-sale, at fair value (cost $54.4 and $50.5, respectively)	88.6	80.3
Other invested assets	5.3	5.3
Notes receivable from affiliate	70.0	70.0
Total investments	2,438.5	2,357.9
Cash and cash equivalents	68.4	86.3
Accrued investment income and other assets	36.1	33.8
Deferred policy acquisition costs (affiliated net assumed $49.6 and $46.8, respectively)	127.4	126.5
Reinsurance recoverable on losses and loss expenses payable	7.9	9.6
Prepaid reinsurance premiums	6.2	6.1
Due from affiliate	0	40.1
Current federal income taxes	0.7	1.1
Net deferred federal income taxes	84.3	97.4
Property and equipment, at cost	7.6	8.1
Total assets	2,777.1	2,766.9
Liabilities and Stockholders’ Equity
Losses and loss expenses payable (affiliated net assumed $504.8 and $494.3, respectively)	997.7	983.2
Unearned premiums (affiliated net assumed $205.4 and $201.7, respectively)	604.2	612.4
Notes payable (affiliates $15.5 and $15.5, respectively)	100.8	100.8
Postretirement and pension benefits (affiliated net ceded $62.3 and $63.2, respectively)	115.6	117.3
Due to affiliate	6.2	0
Other liabilities (affiliated net ceded $2.8 and $5.1, respectively)	48.4	80.3
Total liabilities	1,872.9	1,894.0
Stockholders’ equity:
Common stock, without par value. Authorized 100.0 shares; 47.8 and 47.7 shares issued, respectively, at stated value of $2.50 per share	119.5	119.3
Treasury stock, 6.8 and 6.8 shares, respectively, at cost	(116.1)	(116.0)
Additional paid-in capital	144.5	143.2
Accumulated other comprehensive income (affiliated net ceded $63.7 and $65.1, respectively)	81.0	71.7
Retained earnings	675.3	654.7
Total stockholders’ equity	904.2	872.9
Total liabilities and stockholders’ equity	2,777.1	2,766.9
Class A Preferred Stock [Member]
Stockholders’ equity:
Preferred stock value	0	0
Class B Preferred Stock [Member]
Stockholders’ equity:
Preferred stock value	$ 0	$ 0