Equity Based Compensation Legacy Units (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity-Based Compensation Information [Line Items]
Number of different classes of membership interests prior to the Recapitalization Transactions	7
New Class A Units Attributable to Equity Based Compensation [Roll Forward]
Shares of the Company's Class B common stock for each New Class A Unit	1
Price per share of Class A common stock sold in the IPO	16.00
New Class A Units Attributable to Equity-Based Compensation [Member]
New Class A Units Attributable to Equity Based Compensation [Roll Forward]
Beginning of period	867,000	1,530,000	3,231,000
Exercised, redeemed or exchanged	(867,000)	(653,000)	(1,666,000)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	0	(10,000)	(35,000)
End of period	0	867,000	1,530,000
New Class A Units Attributable to Equity-Based Compensation [Member] | Minimum Number of Years [Member]
New Class A Units Attributable to Equity Based Compensation [Roll Forward]
Number of years after which restrictions lapse	4 years
New Class A Units Attributable to Equity-Based Compensation [Member] | Maximum Number of Years [Member]
New Class A Units Attributable to Equity Based Compensation [Roll Forward]
Number of years after which restrictions lapse	5 years