Consolidated Statement of Stockholders' Equity Statement (USD $) In Thousands, unless otherwise specified	Total	Common Stock Class A [Member]	Common Stock Class B [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
Common stock, shares, outstanding at Dec. 31, 2009	40,264	27,290	12,974
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	30,241	0	0	0	707	16,765	12,769
Issuance of Class A common stock for follow-on offering, value	(3)	0	0	(3)	0	0	0
Issuance of Class A common stock for follow-on offering, shares		0	0
Issuance of Class A common stock for acquisitions	2,535	2	0	1,798	0	0	735
Issuance of Class A common stock for acquisitions, shares	176	176	0
Exchange of New Class A Units, value	(1)	(18)	0	(17)	0	0	0
Exchange of New Class A Units to shares of Class A common stock, shares	0	1,788	(1,788)
Net issuance of restricted stock awards, value	(2,771)	(16)	0	(1,920)	0	0	(867)
Net issuance of restricted stock awards, shares	1,596	1,596	0
Adjustments to Tax Receivable Agreement as a result of the exchange of New Class A Units	1,529	0	0	1,529	0	0	0
Issuance for exercises of IPO Options	282	0	0	203	0	0	79
Issuance of Class A common stock for exercises of stock options, shares	18	18	0
Forfeitures	(2)	(2)	0	0	0	0	0
Forfeitures, shares	(286)	(251)	(35)
Equity-based compensation	20,615	0	0	14,216	0	0	6,399
Income tax benefit on equity-based compensation	(64)	0	0	(64)	0	0	0
Distributions to noncontrolling unitholders	(10,109)	0	0	(7,131)	0	0	(2,978)
Change in ownership interests between periods	0	0	0	(21,403)	0	0	21,403
Deferred tax asset effective tax rate conversion	(786)	0	0	(382)	0	0	(404)
Repurchase of Class A common stock pursuant to publicly announced program, value	(6,110)	(5)	0	(4,198)	0	0	(1,907)
Repurchase of Class A common stock pursuant to publicly announced program, shares	(451)	(451)	0
Dividends on Class A common stock	(6,551)	0	0	0	0	(6,551)	0
Balance at Dec. 31, 2010	342,564	302	1	232,644	1,400	16,923	91,294
Common stock, shares, outstanding at Dec. 31, 2010	41,317	30,166	11,151
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	28,193	0	0	0	(1,113)	18,614	10,692
Issuance of Class A common stock for acquisitions	15,487	12	0	11,512	0	0	3,963
Issuance of Class A common stock for acquisitions, shares	1,180	1,180	0
Exchange of New Class A Units, value	(1)	(6)	0	(7)	0	0	0
Exchange of New Class A Units to shares of Class A common stock, shares	0	653	653
Net issuance of restricted stock awards, value	(4,984)	(19)	0	(3,693)	0	0	(1,310)
Net issuance of restricted stock awards, shares	1,966	1,966	0
Adjustments to Tax Receivable Agreement as a result of the exchange of New Class A Units	821	0	0	821	0	0	0
Issuance for exercises of IPO Options	113	0	0	83	0	0	30
Issuance of Class A common stock for exercises of stock options, shares	7	7	0
Forfeitures	(3)	(3)	0	0	0	0	0
Forfeitures, shares	(312)	(302)	(10)
Equity-based compensation	22,187	0	0	16,474	0	0	5,713
Income tax benefit on equity-based compensation	963	0	0	963	0	0	0
Distributions to noncontrolling unitholders	(8,407)	0	0	(6,256)	0	0	(2,151)
Change in ownership interests between periods	0	0	0	(17,204)	0	0	17,204
Deferred tax asset effective tax rate conversion	553	0	0	516	0	0	37
Repurchase of Class A common stock pursuant to publicly announced program, value	(23,887)	(20)	0	(17,689)	0	0	(6,178)
Repurchase of Class A common stock pursuant to publicly announced program, shares	(2,024)	(2,024)	0
Dividends on Class A common stock	(9,906)	0	0	0	0	(9,906)	0
Balance at Dec. 31, 2011	363,693	316	1	252,572	287	25,631	84,886
Common stock, shares, outstanding at Dec. 31, 2011	42,134	31,646	10,488
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	28,540	0	0	0	2,333	22,264	3,943
Issuance of Class A common stock for follow-on offering, value	49,244	37	0	36,785	0	0	12,422
Issuance of Class A common stock for follow-on offering, shares	3,707	3,707	0
Issuance of Class A common stock for acquisitions	3,079	2	0	2,928	0	0	149
Redemption of New Class A Units, shares	(4,407)	0	(4,407)
Redemption of New Class A Units, value	(58,972)	0	(1)	(44,170)	0	0	(14,801)
Issuance of Class A common stock for acquisitions, shares	227	227	0
Exchange of New Class A Units, value	0	(61)	0	(61)	0	0	0
Exchange of New Class A Units to shares of Class A common stock, shares	0	6,081	(6,081)
Net issuance of restricted stock awards, value	(5,265)	(13)	0	(4,094)	0	0	(1,184)
Net issuance of restricted stock awards, shares	1,315	1,315	0
Adjustments to Tax Receivable Agreement as a result of the exchange of New Class A Units	615	0	0	615	0	0	0
Issuance for exercises of IPO Options	16	0	0	15	0	0	1
Issuance of Class A common stock for exercises of stock options, shares	1	1	0
Forfeitures	(2)	(2)	0	0	0	0	0
Forfeitures, shares	(248)	(248)	0
Equity-based compensation	25,434	0	0	22,613	0	0	2,821
Income tax benefit on equity-based compensation	836	0	0	836	0	0	0
Distributions to noncontrolling unitholders	(3,948)	0	0	(3,661)	0	0	(287)
Change in ownership interests between periods	0	0	0	(87,748)	0	0	87,748
Deferred tax asset effective tax rate conversion	4,411	0	0	4,402	0	0	9
Repurchase of Class A common stock pursuant to publicly announced program, value	(4,002)	(3)	0	(3,783)	0	0	(216)
Adjustments to APIC for Capital Deemed Contributed	(118)	0	0	(113)	0	0	(5)
Repurchase of Class A common stock pursuant to publicly announced program, shares	(309)	(309)	0
Dividends on Class A common stock	(13,616)	0	0	0	0	(13,616)	0
Balance at Dec. 31, 2012	$ 390,181	$ 424	$ 0	$ 352,858	$ 2,620	$ 34,279	$ 0
Common stock, shares, outstanding at Dec. 31, 2012	42,420	42,420	0