Dividends from Subsidiaries and Statutory Financial Information - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Statutory Accounting Practices [Line Items]
Maximum amount available for the payment of dividends without prior regulatory approval	$ 59,200,000
Dividends paid to Parent Company	45,000,000	40,000,000	25,000,000
Statutory net income	16,300,000	85,700,000	44,500,000
Statutory surplus	$ 662,200,000	$ 686,900,000
Minimum
Statutory Accounting Practices [Line Items]
Insurance examination period	3 years
Maximum
Statutory Accounting Practices [Line Items]
Insurance examination period	5 years