Derivative Instruments in CLOs - Net Realized and Unrealized Appreciation (Depreciation) on Derivative instruments Included in Net Investment Gains (Loss) of Consolidated Funds (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Derivative Instruments, Gain (Loss) [Line Items]
Realized Appreciation (Depreciation)	$ 1.8	$ 17.4	$ 22.2
Change in Unrealized Appreciation (Depreciation)	(24.4)	(10.8)	(72.2)
Total	(22.6)	6.6	(50.0)
Cross-currency swap contract (s) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Appreciation (Depreciation)	1.9	17.5	22.3
Change in Unrealized Appreciation (Depreciation)	(21.4)	(9.4)	(75.5)
Total	(19.5)	8.1	(53.2)
Currency option (s) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Appreciation (Depreciation)	(0.1)	(0.1)	(0.1)
Change in Unrealized Appreciation (Depreciation)	(2.9)	(1.2)	4.4
Total	(3.0)	(1.3)	4.3
Interest rate cap contract (s) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Appreciation (Depreciation)
Change in Unrealized Appreciation (Depreciation)	(0.1)	(0.1)	0.1
Total	(0.1)	(0.1)	0.1
Credit risk swap contract (s) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Realized Appreciation (Depreciation)
Change in Unrealized Appreciation (Depreciation)		(0.1)	(1.2)
Total		$ (0.1)	$ (1.2)