Condensed Consolidated Statement of Stockholders' Equity and Comprehensive Income Statement (USD $) In Thousands	Total	Common Class A [Member]	Common Class B [Member]	Comprehensive Income [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Noncontrolling Interest [Member]
Balance at Dec. 31, 2009	$ 313,757	$ 273	$ 1		$ 207,210	$ 693	$ 6,709	$ 98,871
Balance, shares at Dec. 31, 2009		27,290	12,974
Comprehensive income
Net income for the nine months ended September 30	19,383	0	0	19,383	0	0	10,889	8,494
Currency translation adjustment	(238)	0	0	(238)	0	(155)	0	(83)
Amortization of post-retirement benefits, net of tax	39	0	0	39	0	26	0	13
Total comprehensive income	19,184	0	0	19,184	0	(129)	10,889	8,424
Sale of Class A common stock	(3)	0	0		(3)	0	0	0
Issuance of Class A common stock for acquisitions	1,204	1	0		827	0	0	376
Issuance of Class A common stock for acquisitions, shares		93	0
Exchange of New Class A Units	0	0	0		0	0	0	0
Exchange of New Class A Units, shares		45	(45)
Net issuance of restricted stock awards	(2,577)	13	0		(1,777)	0	0	(813)
Net issuance of restricted stock awards, shares		1,354	0
Adjustments to Tax Receivable Agreement as a result of the exchange of New Class A Units	62	0	0		62	0	0	0
Issuance for exercises of IPO Options	66	0	0		45	0	0	21
Issuance for exercises of IPO Options, shares		4	0
Forfeitures	(2)	(2)	0		0	0	0	0
Forfeitures, shares		(222)	(31)
Equity-based compensation	16,316	0	0		11,178	0	0	5,138
Income tax windfall/(shortfall) on equity-based compensation	72	0	0		72	0	0	0
Distributions to noncontrolling unitholders	(5,480)	0	0		(3,755)	0	0	(1,725)
Change in ownership interests between periods	0	0	0		4,113	0	0	(4,113)
Deferred tax asset effective tax rate conversion	(1,411)	0	0		(1,007)	0	0	(404)
Repurchase of Class A common stock pursuant to publicly announced program	(6,017)	(4)	0		(4,131)	0	0	(1,882)
Repurchase of Class A common stock pursuant to publicly announced program, shares		(444)	0
Dividends on Class A common stock	(4,778)	0	0		0	0	(4,778)	0
Balance at Sep. 30, 2010	330,393	281	1		212,834	564	12,820	103,893
Balance, shares at Sep. 30, 2010		28,120	12,898
Balance at Dec. 31, 2010	342,564	302	1		232,644	1,400	16,923	91,294
Balance, shares at Dec. 31, 2010		30,166	11,151
Comprehensive income
Net income for the nine months ended September 30	18,574	0	0	18,574	0	0	11,569	7,005
Currency translation adjustment	(307)	0	0	(307)	0	(209)	0	(98)
Amortization of post-retirement benefits, net of tax	(81)	0	0	(81)	0	(61)	0	(20)
Total comprehensive income	18,186	0	0	18,186	0	(270)	11,569	6,887
Issuance of Class A common stock for acquisitions	2,925	2	0		2,174	0	0	749
Issuance of Class A common stock for acquisitions, shares		224	0
Exchange of New Class A Units	(1)	3	0		(4)	0	0	0
Exchange of New Class A Units, shares		331	(331)
Net issuance of restricted stock awards	(4,874)	16	0		(3,608)	0	0	(1,282)
Net issuance of restricted stock awards, shares		1,666	0
Adjustments to Tax Receivable Agreement as a result of the exchange of New Class A Units	451	0	0		451	0	0	0
Issuance for exercises of IPO Options	113	0	0		83	0	0	30
Issuance for exercises of IPO Options, shares		7	0
Forfeitures	(2)	(2)	0		0	0	0	0
Forfeitures, shares		(233)	(9)
Equity-based compensation	17,422	0	0		12,930	0	0	4,492
Income tax windfall/(shortfall) on equity-based compensation	867	0	0		867	0	0	0
Distributions to noncontrolling unitholders	(4,030)	0	0		(2,981)	0	0	(1,049)
Change in ownership interests between periods	0	0	0		5,503	0	0	(5,503)
Deferred tax asset effective tax rate conversion	406	0	0		371	0	0	35
Repurchase of Class A common stock pursuant to publicly announced program	(19,222)	(16)	0		(14,245)	0	0	(4,961)
Repurchase of Class A common stock pursuant to publicly announced program, shares		(1,615)	0
Dividends on Class A common stock	(7,439)	0	0		0	0	(7,439)	0
Balance at Sep. 30, 2011	$ 347,366	$ 305	$ 1		$ 234,185	$ 1,130	$ 21,053	$ 90,692
Balance, shares at Sep. 30, 2011		30,546	10,811