Other Reinsurance (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended								3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Capitol [Member]	Dec. 31, 2012 ORCC [Member]	Dec. 31, 2012 Capitol [Member]	Dec. 31, 2011 Capitol [Member]	Dec. 31, 2010 Capitol [Member]	Sep. 30, 2012 Capitol [Member] Trinity [Member]	Dec. 31, 2012 Capitol [Member] Trinity [Member]	Dec. 31, 2012 ORCC [Member]	Dec. 31, 2011 ORCC [Member]	Dec. 31, 2010 ORCC [Member]	Dec. 31, 2012 ORCC [Member] Trinity [Member]	Dec. 31, 2012 Other Insurance Businesses and Pools [Member]	Dec. 31, 2011 Other Insurance Businesses and Pools [Member]	Dec. 31, 2010 Other Insurance Businesses and Pools [Member]
Assumed Insurance [Line Items]
Earned Premiums Assumed	$ 44.1	$ 43.7	$ 45.7			$ 25.0	$ 27.9	$ 30.1			$ 8.2	$ 9.0	$ 9.6		$ 10.9	$ 6.8	$ 6.0
Earned Premiums Assumed, Percentage										100.00%				100.00%
Change in Policyholder Benefits and Incurred Losses and LAE as Result of Quota Share Revision									$ (2.6)
Number of Company Employee Board Members				5	9
Number of Board of Director Members				5	9