Quarterly report pursuant to Section 13 or 15(d)

Basic and Diluted Net Earnings Per Share - Additional Information (Detail)

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Basic and Diluted Net Earnings Per Share - Additional Information (Detail)
9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Dec. 31, 2012
Earnings Per Share [Abstract]      
Options to purchase Class A common stock 2,296,020 2,089,524 1,927,099
Dilutive shares 794,553 695,025