Fair Value Measurements - Fair Values of Funds and Unfunded Commitments for Funds (Parenthetical) (Detail)	6 Months Ended
	Jun. 30, 2013
Minimum [Member] | Passive Funds [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Liquidation period of funds, maximum (in years)	1 year
Minimum [Member] | Co-Managed Funds [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Liquidation period of funds, maximum (in years)	2 years
Maximum [Member] | Passive Funds [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Liquidation period of funds, maximum (in years)	7 years
Maximum [Member] | Co-Managed Funds [Member]
Fair Value, Estimate Not Practicable, Financial Statement Captions [Line Items]
Liquidation period of funds, maximum (in years)	5 years