Earnings per share - Weighted Average Number of Shares Used in Computing Earnings Per Share (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share Basic And Diluted Other Disclosures [Abstract]
Average basic shares outstanding	4,817,856	2,610,856	4,816,523	2,610,856
Effect of dilutive securities:
Stock options	2,316	1,402	2,380	1,828
Average diluted shares outstanding	4,820,172	2,612,258	4,818,903	2,612,684
Basic earnings per share	$ 0.13	$ 0.09	$ 0.21	$ 0.17
Diluted earnings per share	$ 0.13	$ 0.09	$ 0.21	$ 0.17