Investments of Operating Entities and Consolidated Funds - Securities Purchased Under Agreements to Resell or Sold Under Agreements to Repurchase (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities purchased under agreements to resell	$ 0	$ 166,260,000
Securities sold under agreements to repurchase	123,839,000	228,783,000
Operating Entities [Member] | Securities Owned at Fair Value [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities pledged by the Company as collateral	130,300,000	243,100,000
Operating Entities [Member] | Fair Value, Inputs, Level 1 [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities received by the Company as collateral		166,700,000
Operating Entities [Member] | Maturity on Demand [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	123,839,000	228,783,000
Operating Entities [Member] | Royal Bank of Canada [Member] | Maturity on Demand [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	29,039,000	49,450,000
Operating Entities [Member] | Royal Bank of Canada [Member] | Minimum [Member] | Maturity on Demand [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on repurchase agreements	2.12%	1.53%
Operating Entities [Member] | Royal Bank of Canada [Member] | Maximum [Member] | Maturity on Demand [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on repurchase agreements	2.20%	1.58%
Operating Entities [Member] | Barclays Capital Inc [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities purchased under agreements to resell		166,260,000
Operating Entities [Member] | Barclays Capital Inc [Member] | Maturity on Demand [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 94,800,000	$ 179,333,000
Operating Entities [Member] | Barclays Capital Inc [Member] | Minimum [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on resell agreements		(0.38%)
Operating Entities [Member] | Barclays Capital Inc [Member] | Minimum [Member] | Maturity on Demand [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on repurchase agreements	0.25%	0.03%
Operating Entities [Member] | Barclays Capital Inc [Member] | Maximum [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on resell agreements		0.25%
Operating Entities [Member] | Barclays Capital Inc [Member] | Maximum [Member] | Maturity on Demand [Member]
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on repurchase agreements	0.27%	0.08%