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)
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Dec. 31, 2012
Earnings Per Share Disclosure [Line Items]      
Options to purchase Class A common stock 2,580,033 2,225,947 1,927,099
Dilutive shares 675,808 188,724