Net Investment Income (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Net Investment Income [Line Items]
Interest income	$ 94,700,000		$ 95,300,000
Dividend income	14,500,000		13,600,000
Investment expenses	(7,300,000)		(7,000,000)
Other investment results	3,600,000		4,300,000
Net investment income	113,382,000		110,583,000
Ares
Net Investment Income [Line Items]
Equity results	2,300,000	[1]	100,000	[1]
ORX
Net Investment Income [Line Items]
Equity results	(1,000,000)		400,000
Pillar Holdings and Funds | Pillar Capital Holdings Limited And Managed Funds
Net Investment Income [Line Items]
Equity results	$ 6,600,000	[1]	$ 3,900,000	[1]

[1] See Note 3(g) for discussion of the Pillar Investments and the investment in Ares, each as defined in Note 3(g).