Summary of Significant Accounting Principles - Additional Information (Detail) (USD $)	9 Months Ended
	Sep. 30, 2012 Location
Significant Accounting Policies [Line Items]
Par value of common stock outstanding	1.00
Transatlantic
Significant Accounting Policies [Line Items]
Business acquisition date	Mar. 06, 2012
Number of states entity operates	50
Transatlantic | United States
Significant Accounting Policies [Line Items]
Number of operating locations excluding headquarters	6
Transatlantic | United Kingdom and Europe
Significant Accounting Policies [Line Items]
Number of operating locations excluding headquarters	7
Transatlantic | Central and South America
Significant Accounting Policies [Line Items]
Number of operating locations excluding headquarters	3
Transatlantic | Asia
Significant Accounting Policies [Line Items]
Number of operating locations excluding headquarters	3
Minimum
Significant Accounting Policies [Line Items]
Useful life of property and equipment	3 years
Maximum
Significant Accounting Policies [Line Items]
Useful life of property and equipment	20 years
Investment in Homesite
Significant Accounting Policies [Line Items]
Ownership interest percentage	33.00%
ORX Exploration, Incorporated
Significant Accounting Policies [Line Items]
Ownership interest percentage	38.00%