Background (Details) (USD $)	0 Months Ended			0 Months Ended					0 Months Ended
	Feb. 07, 2011	Jun. 30, 2012	Dec. 31, 2011	Feb. 07, 2011 IPO [Member]	Feb. 01, 2011 IPO [Member]	Feb. 01, 2011 Corporate [Member] IPO [Member]	Feb. 01, 2011 Investor [Member] IPO [Member]	Feb. 03, 2011 Overallotment Option [Member] IPO [Member]	Feb. 07, 2011 Common Class B [Member] IPO [Member]
Organization, Consolidation and Presentation of Financial Statements [Line Items]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)		100,000,000	100,000,000	100,000,000	5,360,000			804,000
Preferred stock, shares authorized		10,000,000	10,000,000	10,000,000
Common stock, par value (in dollars per share)		$ 0.001	$ 0.001	$ 0.001
Sale of stock, price per share (in dollars per share)					$ 16			$ 16
Common Stock, Value, Issued		$ 25,000	$ 24,000		$ 85,800,000	$ 57,200,000	$ 28,600,000	$ 12,900,000
Proceeds from Issuance Initial Public Offering				62,200,000
Common Stock Underwriting and Commissions Expense				4,900,000
Other Expenses				3,000,000
Dividends, Common Stock									$ 29,600,000
Stock Issued During Period, Shares, Conversion of Convertible Securities				11,089,201
Common stock, shares issued		24,761,000	24,370,000			3,574,285	1,785,715
Stock Issued During Period, Shares, Reverse Stock Splits	0.786