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The Company - Additional Information (Detail) (USD $)	12 Months Ended
The Company - Additional Information (Detail) (USD $)	Dec. 31, 2011	Jun. 02, 2011 IPO	Jun. 02, 2011 Redeemable convertible preferred stock	Jun. 02, 2011 Series B preferred stock
Issuance of common stock at public offering	12,021,250
Common stock issuance price		$ 18.00
Proceeds from issuance of common stock	$ 201,236,000
Underwriting discounts and commissions	15,100,000
Initial public offering costs	$ 4,295,000
Redeemable convertible preferred stock converted to shares of common stock			34,534,125	303,855

Number of shares issued for each share of convertible preferred stock that is converted.

The cash inflow associated with the amount received from entity's first offering of stock to the public.

Number of new stock issued during the period.