Organization, Description of Business (Details) (Common Stock, USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended
	Aug. 31, 2011 Initial public offering	Aug. 31, 2011 Initial public offering Underwriter option	Apr. 30, 2012 April 2012 public offering	Apr. 30, 2012 April 2012 public offering Underwriter option
Public Offerings
Issuance of shares, net of issuance costs (in shares)	7,500,000		2,200,000
Price to the public (in dollars per share)	$ 10.00		$ 18.50
Proceeds from initial public offering, net of underwriting discounts and commissions and other offering costs	$ 66.0		$ 38.5
Offering costs	$ 3.8		$ 0.7
Stock sold by certain existing stockholders (in shares)	2,585,500	1,315,500	7,000,000	1,200,000