Investment Securities - Investment Securities (Parenthetical) (Detail)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Amortized Cost And Fair Value Debt Securities [Abstract]
Federal statutory rate	35.00%	35.00%
Weighted-average maturity of available-for-sale investment securities	5 years 6 months		4 years 1 month 6 days
Weighted-average yield of available-for-sale investment securities	2.70%		2.93%
Weighted average maturity of held-to-maturity investment securities	4 years 2 months 12 days		3 years 3 months 18 days
Weighted-average yield of held-to-maturity investment securities	1.97%		1.94%