Impairment of Investment Securities - Cumulative Roll Forward of Credit Losses Recognized in Earnings for Debt Securities Held and Not Intended to be Sold (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013		Sep. 30, 2012
Impairment of Investment Securities Disclosure [Abstract]
Balance, beginning (a)	$ 42,699	$ 44,230	$ 43,274	[1]	$ 44,736	[1]
Credit losses on debt securities for which other-than-temporary impairment was not previously recognized	0	0	0		0
Additional credit losses on debt securities for which other-than-temporary impairment was previously recognized	0	0	0		0
Increases in cash flows expected to be collected, recognized over the remaining life of the security (b)	(1,326)	436	(1,901)	[2]	(942)	[2]
Balance, ending	$ 41,373	$ 43,794	$ 41,373		$ 43,794

[1] The beginning balance represents credit related losses included in other-than-temporary impairment charges recognized on debt securities in prior periods.

[2] Represents the increase in cash flows recognized in interest income during the period.