Securities - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Jul. 31, 2013	Sep. 30, 2013 Securities	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Transfer of securities from available-for-sale to held-to-maturity	$ 39,000,000	$ 38,930,000
unrealized losses on Transfer of securities from available-for-sale to held-to-maturity	1,900,000
Carrying value of securities		89,500,000	79,200,000
Restricted stock investment in FHLB stock		5,000,000	5,000,000
Federal Reserve Bank stock		$ 471,000	$ 471,000
Number of securities in unrealized loss		68
Number of securities in continuous loss		3