Net Investment Income (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Net Investment Income [Line Items]
Interest income	$ 96,200,000		$ 88,400,000		$ 288,900,000		$ 257,700,000
Dividend income	15,800,000		13,300,000		46,000,000		41,100,000
Investment expenses	(7,200,000)		(5,300,000)		(21,600,000)		(15,600,000)
Other investment results	5,700,000		1,200,000		12,000,000		4,400,000
Net investment income	118,284,000		115,287,000		342,961,000		334,501,000
Homesite
Net Investment Income [Line Items]
Equity results			7,700,000	[1]			32,200,000	[1]
ORX
Net Investment Income [Line Items]
Equity results	100,000		(2,300,000)		(600,000)		(1,900,000)
Ares Management Limited Liability Company
Net Investment Income [Line Items]
Net investment income	2,700,000	[2]	2,900,000	[2]	5,800,000	[2]	2,900,000	[2]
Pillar Holdings and Funds | Pillar Capital Holdings Limited And Managed Funds
Net Investment Income [Line Items]
Equity results	$ 5,000,000	[2]	$ 9,400,000	[2]	$ 12,500,000	[2]	$ 13,700,000	[2]

[1] Homesite was sold on December 31, 2013.

[2] See Note 3(g) for discussion of the Pillar Investments and the investment in Ares.