Investments of Operating Entities and Consolidated Funds - Securities Purchased Under Agreements to Resell or Sold Under Agreements to Repurchase (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 29,241,000	$ 165,945,000
Operating Entities | Securities Owned at Fair Value
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities pledged by the Company as collateral	36,200,000	173,700,000
Operating Entities | Maturity on Demand
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	29,241,000	165,945,000
Operating Entities | Royal Bank of Canada | Maturity on Demand
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	29,241,000	29,039,000
Operating Entities | Royal Bank of Canada | Minimum | Maturity on Demand
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on repurchase agreements	1.74%	2.12%
Operating Entities | Royal Bank of Canada | Maximum | Maturity on Demand
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on repurchase agreements	2.10%	2.20%
Operating Entities | Barclays Capital Inc
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities purchased under agreements to resell		0
Operating Entities | Barclays Capital Inc | Maturity on Demand
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase		$ 136,906,000
Operating Entities | Barclays Capital Inc | Minimum | Maturity on Demand
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on repurchase agreements		(0.05%)
Operating Entities | Barclays Capital Inc | Maximum | Maturity on Demand
Assets Purchased Under Agreements to Resell or Sold under Agreements to Repurchase [Line Items]
Interest rates on repurchase agreements		0.23%