Summary Of Cumulative Amounts Related To Credit Loss Portion Of OTTI Losses On Debt Securities (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Beginning balance	$ 3,332	$ 1,885	$ 3,321	$ 1,658
Additions for credit loss impairments recognized in the current period on securities not previously impaired		623		850
Additions for credit loss impairments recognized in the current period on securities previously impaired			11
Reductions for credit loss impairments previously recognized on securities sold during the period
Ending balance	$ 3,332	$ 2,508	$ 3,332	$ 2,508