Earning Per Share - Additional Information (Detail)	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Earnings Per Share [Line Items]
Options for aggregate common shares	232,000	232,000	197,000	197,000	197,000
Dilutive stock options	4,764	4,209