Equity Based Compensation Equity-Based Compensation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity-Based Compensation [Line Items]
Equity-based compensation	$ 25,537	$ 21,884	$ 20,444
Equity-based compensation from Legacy Units and IPO Options [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	22	207	3,399
Equity-based compensation from Ongoing RSAs [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	25,515	21,677	17,045
Compensation and benefits [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	19,098	17,086	14,891
Compensation and benefits [Member] | Equity-based compensation from Legacy Units and IPO Options [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	(43)	(273)	1,308
Compensation and benefits [Member] | Equity-based compensation from Ongoing RSAs [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	19,141	17,359	13,583
Acquisition retention expenses [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	2,908	1,054	11
Acquisition retention expenses [Member] | Equity-based compensation from Legacy Units and IPO Options [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	0	0	0
Acquisition retention expenses [Member] | Equity-based compensation from Ongoing RSAs [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	2,908	1,054	11
Selling, general and administrative [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	3,531	3,744	5,542
Selling, general and administrative [Member] | Equity-based compensation from Legacy Units and IPO Options [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	65	480	2,091
Selling, general and administrative [Member] | Equity-based compensation from Ongoing RSAs [Member]
Equity-Based Compensation [Line Items]
Equity-based compensation	$ 3,466	$ 3,264	$ 3,451