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 six months ended June 30	12,186	0	0	12,186	0	0	6,780	5,406
Currency translation adjustment	(3,083)	0	0	(3,083)	0	(2,106)	0	(977)
Amortization of post-retirement benefits, net of tax	27	0	0	27	0	18	0	9
Total comprehensive income	9,130	0	0	9,130	0	(2,088)	6,780	4,438
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		43	(43)
Net issuance of restricted stock awards	(2,483)	14	0		(1,713)	0	0	(784)
Net issuance of restricted stock awards, shares		1,336	0
Adjustments to Tax Receivable Agreement as a result of the exchange of New Class A Units	61	0	0		61	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		(174)	(22)
Equity-based compensation	11,928	0	0		8,169	0	0	3,759
Income tax windfall/(shortfall) on equity-based compensation	72	0	0		72	0	0	0
Distributions to noncontrolling unitholders	(2,135)	0	0		(1,462)	0	0	(673)
Change in ownership interests between periods	0	0	0		4,103	0	0	(4,103)
Deferred tax asset effective tax rate conversion	(147)	0	0		253	0	0	(400)
Repurchase of Class A common stock pursuant to publicly announced program	(5,302)	(4)	0		(3,641)	0	0	(1,657)
Repurchase of Class A common stock pursuant to publicly announced program, shares		(384)	0
Dividends on Class A common stock	(3,108)	0	0		0	0	(3,108)	0
Balance at Jun. 30, 2010	323,038	282	1		213,921	(1,395)	10,381	99,848
Balance, shares at Jun. 30, 2010		28,208	12,909
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 six months ended June 30	12,138	0	0	12,138	0	0	7,537	4,601
Currency translation adjustment	2,252	0	0	2,252	0	1,709	0	543
Amortization of post-retirement benefits, net of tax	(79)	0	0	(79)	0	(60)	0	(19)
Total comprehensive income	14,311	0	0	14,311	0	1,649	7,537	5,125
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		332	(332)
Net issuance of restricted stock awards	(4,696)	17	0		(3,477)	0	0	(1,236)
Net issuance of restricted stock awards, shares		1,674	0
Adjustments to Tax Receivable Agreement as a result of the exchange of New Class A Units	373	0	0		373	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	(1)	(1)	0		0	0	0	0
Forfeitures, shares		(130)	(1)
Equity-based compensation	12,091	0	0		8,970	0	0	3,121
Income tax windfall/(shortfall) on equity-based compensation	911	0	0		911	0	0	0
Distributions to noncontrolling unitholders	(2,101)	0	0		(1,551)	0	0	(550)
Change in ownership interests between periods	0	0	0		6,888	0	0	(6,888)
Deferred tax asset effective tax rate conversion	426	0	0		390	0	0	36
Repurchase of Class A common stock pursuant to publicly announced program	(8,936)	(7)	0		(6,619)	0	0	(2,310)
Repurchase of Class A common stock pursuant to publicly announced program, shares		(625)	0
Dividends on Class A common stock	(4,969)	0	0		0	0	(4,969)	0
Balance at Jun. 30, 2011	$ 353,010	$ 316	$ 1		$ 240,782	$ 3,049	$ 19,491	$ 89,371
Balance, shares at Jun. 30, 2011		31,648	10,818