Class A Common Shares Reserved for Future Issuance (Detail) (Class A Common Stock)	Dec. 31, 2012
Class of Stock [Line Items]
Total shares reserved for future issuance	7,062,450
Stock Option
Class of Stock [Line Items]
Total shares reserved for future issuance	1,662,450
Class B Common Stock Converted Into Class A Common Stock
Class of Stock [Line Items]
Total shares reserved for future issuance	5,400,000