Statements of Shareholders’ Equity (Deficit) (USD $) In Thousands, unless otherwise specified	Total	Class A Common Stock	Class B Common Stock	Common Stock	Non-Voting Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings (Accumulated Deficit)
Balance at Dec. 31, 2009	$ (178,127)	$ 2	$ 1			$ 107		$ (178,237)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share-based compensation	569					569
Net income	72,481							72,481
Balance at Dec. 31, 2010	(105,077)	2	1	0	0	676	0	(105,756)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of Class A & B common stock to common stock		(2)	(1)	3
Proceeds from initial public offering, net	170,828			1		170,827
Conversion of debt to common stock	279,206			2		279,204
Conversion of preferred stock to common stock	81,747			1		81,746
Record liability under Tax Receivable Agreement	(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
Proceeds from options exercised	423					423
Net income	76,448							76,448
Other	9					9
Balance at Dec. 31, 2011	466,706	0	0	6	1	496,136	(129)	(29,308)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adjustment to liability recorded under Tax Receivable Agreement	1,497					1,497
Share-based compensation	4,327					4,327
Repurchase of common stock	(1,022)						(1,022)
Proceeds from options exercised	469					469
Tax benefit of options exercised	2,098					2,098
Net income	108,460							108,460
Balance at Dec. 31, 2012	$ 582,535	$ 0	$ 0	$ 6	$ 1	$ 504,527	$ (1,151)	$ 79,152