Summary of Significant Accounting Policies (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended		3 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2012	Jan. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012	Dec. 31, 2011	Mar. 31, 2012
Revision [Abstract]
Cumulative impact of prior period reclassification adjustment							$ 8,800,000
Impact of revision on cash flows						5,700,000
Cash Distributions [Abstract]
Subsequent cash distribution, declaration date			Oct. 24, 2012
Subsequent cash distribution, amount			37,900,000
Subsequent cash distribution, distribution declared (in dollars per unit)			$ 0.36
Subsequent cash distribution, distribution date			Nov. 21, 2012
Subsequent cash distribution, date of record			Nov. 05, 2012
Deferred Compensation Plans [Abstract]
Vesting period of awards					4 years
Employee allocation percentage maximum (in hundredths)			50.00%		50.00%
Deferred cash maximum per employee			250,000		250,000
One-time, non-cash deferred compensation charge				587,100,000
Percentage of unrecognized deferred incentive compensation expense recognized (in hundredths)				100.00%		100.00%
Deferred compensation liability for the full dollar value of the awards				159,900,000		159,900,000
Restricted holding unit awards to employees (in units)	2.7	8.7			11.9	8.7
Reclassified liability to partners' capital		130,300,000
Holding units purchased in period (in units)			2.9		9.5
Dollar amount paid for holding units acquired			39,800,000		134,900,000
Open-market purchases of holding units (in units)			2.8		9.2
Dollar amount paid for open-market purchases of holding units			$ 38,800,000		$ 129,400,000
Unallocated holding units remaining in the consolidated Rabbi Trust (in units)			11.8		11.8