Common Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Jul. 23, 2012	Feb. 29, 2012
Class of Stock [Line Items]
Common stock sold	9,775,000
Selling price per share	$ 15.40
Gross proceeds raised from the sale of common stock	$ 55.8
Net proceeds from the sale of our common stock	51.9
Underwriting discounts and commissions	2.7
Other offering expenses	$ 1.2
Shares Offered By Company
Class of Stock [Line Items]
Common stock sold	3,625,000
Shares Offered By Selling Stockholders
Class of Stock [Line Items]
Common stock sold	6,150,000
IPO
Class of Stock [Line Items]
Common stock sold		10,906,941
Selling price per share		$ 12
Gross proceeds raised from the sale of common stock		$ 125.1
Net proceeds from the sale of our common stock		112.8
Underwriting discounts and commissions		8.8
Other offering expenses		$ 3.5
IPO | Shares Offered By Company
Class of Stock [Line Items]
Common stock sold		10,422,645
IPO | Shares Offered By Selling Stockholders
Class of Stock [Line Items]
Common stock sold		484,296