Debt (Trust Preferred Securities) (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	9 Months Ended
	Mar. 28, 2011 Mercer Insurance Group [Member] issues	Sep. 30, 2012 Trust Preferred Securities [Member]
Extinguishment of Debt [Line Items]
Number of issuances of Trust Preferred Securities assumed with our acquisition of Mercer Insurance Group	3
Outstanding balance of the Trust Preferred Securities assumed with our acquisition of Mercer Insurance Group	$ 15.6
Interest expense incurred		$ 0.5