Statements Of Shareholders' Equity (USD $) In Thousands	Total	Class A Common Stock [Member]	Class B Common Stock [Member]	Common Stock [Member]	Nonvoting Common Stock [Member]	Additional Paid-In Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2008	$ (261,890)	$ 2	$ 1			$ 50	$ (13)	$ (261,930)
Share-based compensation	113					113
Repurchase of common stock	(43)						(43)
Retirement of common stock						(56)	56
Net income	83,693							83,693
Balance at Dec. 31, 2009	(178,127)	2	1			107	0	(178,237)
Share-based compensation	569					569
Net income	72,481							72,481
Balance at Dec. 31, 2010	(105,077)	2	1			676	0	(105,756)
Conversion of Class A & B common stock to common stock (unaudited)		(2)	(1)	3
Proceeds from initial public offering, net (unaudited)	170,828			1		170,827
Conversion of debt to common stock (unaudited)	279,206			2		279,204
Conversion of preferred stock to common stock (unaudited)	81,747			1		81,746
Record liability under Tax Receivable Agreement (unaudited)	(36,522)					(36,522)
Share-based compensation	530					530
Repurchase of common stock	(886)					(757)	(129)
Conversion of common stock to non-voting common stock				(1)	1
Options exercised (unaudited)	423					423
Net income	76,448							76,448
Other (unaudited)	9					9
Balance at Dec. 31, 2011	$ 466,706			$ 6	$ 1	$ 496,136	$ (129)	$ (29,308)