Investment Securities - Roll Forward of Credit Losses on Securities (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Investments Debt And Equity Securities [Abstract]
Cumulative credit losses, Beginning Balance	$ 63,114
Additions for credit losses on securities for which OTTI was not previously recognized	137
Additions for additional credit losses on securities for which OTTI was previously recognized	834
Cumulative credit losses, Ending Balance	$ 64,085