Intangible Assets and Goodwill - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Goodwill [Line Items]
Goodwill	$ 38,300,000		$ 38,300,000	$ 47,500,000
Amount of redemption notices related to Credit Hedge Funds		$ 1,900,000,000
Impairment of intangible assets			186,600,000
Total net pretax charge Credit Hedge Funds			162,400,000
Impairment loss			11,800,000	66,200,000	$ 20,800,000
Intangible asset amortization expense			76,100,000	103,000,000	$ 117,900,000
Corporate Private Equity
Goodwill [Line Items]
Goodwill	0		0
Investment Solutions
Goodwill [Line Items]
Goodwill	10,300,000		10,300,000	19,500,000
Impairment of intangible assets	15,000,000
Global Market Strategies
Goodwill [Line Items]
Goodwill	$ 28,000,000		$ 28,000,000	$ 28,000,000
Minimum | Discounted Cash Flow | Level III | Global Market Strategies
Goodwill [Line Items]
Discount rate (as a percent)			10.00%
Maximum | Discounted Cash Flow | Level III | Global Market Strategies
Goodwill [Line Items]
Discount rate (as a percent)			20.00%