Derivative Instruments in CLOs - Gross Fair Value Amounts of Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Fair value- assets	$ 13.0	$ 26.7
Fair value - liabilities	(21.5)	(5.9)
Currency option (s) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	184.8	181.3
Fair value- assets	7.3	10.0
Fair value - liabilities
Interest rate cap contract (s) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	36.0	32.0
Fair value- assets		0.1
Fair value - liabilities
Cross-currency swap contract (s) [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount	274.5	272.7
Fair value- assets	5.7	16.6
Fair value - liabilities	$ (21.5)	$ (5.9)