Summary of Cumulative Amounts Related to Credit Loss Portion of the OTTI Losses on Debt Securities (Detail) (USD $) In Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Beginning balance	$ 1,669	$ 2,577	$ 1,658	$ 2,523
Credit losses on securities not previously impaired at the beginning of the period		182		236
Additional credit losses on securities previously impaired at the beginning of the period	215		226
Reductions for securities sold during the period
Ending balance	$ 1,884	$ 2,759	$ 1,884	$ 2,759