Securities - Additional Information (Detail) (USD $)	6 Months Ended	12 Months Ended
	Jun. 30, 2013 Securities	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Carrying value of securities	$ 87,300,000	$ 79,200,000
Restricted stock investment in FHLB stock	5,000,000	5,000,000
Federal Reserve Bank stock	471,000	471,000
Income tax provision applicable to realized gains	3,000	0
Income tax benefit on realized losses	$ 0	$ 0
Number of securities in unrealized loss	60
Number of securities in continuous loss	5