Summary of Significant Accounting Principles - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2013 Location
Homesite
Significant Accounting Policies [Line Items]
Ownership interest percentage	33.00%
ORX Exploration, Incorporated
Significant Accounting Policies [Line Items]
Ownership interest percentage	38.00%
TransRe
Significant Accounting Policies [Line Items]
Business acquisition date	Mar. 06, 2012
Number of states entity operates	50
TransRe | United States
Significant Accounting Policies [Line Items]
Number of operating locations excluding headquarters	6
TransRe | United Kingdom and Europe
Significant Accounting Policies [Line Items]
Number of operating locations excluding headquarters	7
TransRe | Central and South America
Significant Accounting Policies [Line Items]
Number of operating locations excluding headquarters	3
TransRe | Asia
Significant Accounting Policies [Line Items]
Number of operating locations excluding headquarters	3