Subsequent Events (unaudited) (Details) (USD $)	6 Months Ended			0 Months Ended		0 Months Ended				0 Months Ended
	Jun. 30, 2012		Apr. 30, 2012	Aug. 01, 2012 Subsequent Event [Member]	Jul. 19, 2012 Subsequent Event [Member]	Aug. 01, 2012 Common Class A [Member] Subsequent Event [Member]	Jul. 25, 2012 Common Class A [Member] Subsequent Event [Member]	Jun. 30, 2012 Common Stock	Dec. 31, 2011 Common Stock	Jul. 19, 2012 Common Stock Subsequent Event [Member]	Jul. 25, 2012 IPO [Member] Subsequent Event [Member]	Jul. 25, 2012 IPO [Member] Common Class A [Member] Subsequent Event [Member]	Jul. 25, 2012 IPO [Member] Common Class B [Member] Subsequent Event [Member]
Subsequent Event [Line Items]
Sale of common stock (shares)												4,025,000
Options granted, weighted average exercise price (usd per share)	$ 25.03	[1]								$ 26		$ 26
Proceeds from issuance of initial public offering											$ 97,300,000
Cash paid for expenses in connection with initial public offering											3,800,000
Common stock, shares issued								7,096,909	7,025,467				33,864,565
Options granted, number of shares	626,500	[1]								1,300,000
Estimated rate of stock options vested					25.00%
Total unrecognized estimated compensation expense, non-vested options					14,800,000
Shares issued during the period (shares)							308,032
Number of shares entited by rights issued			352,178				352,178
Exercise price of rights (usd per share)			26				26
Issuance of common stock, shares						231,695
Proceeds from issuance of common stock				$ 6,000,000

[1] Includes 242,500 shares granted to non-employees. The assumptions used to value these grants are similar to those used for grants made to employees with the exception of the expected term.