Net Investment Income (Detail) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Net Investment Income [Line Items]
Interest income	$ 97,400,000		$ 85,900,000		$ 192,700,000		$ 169,300,000
Dividend income	19,800,000		12,700,000		33,300,000		27,800,000
Investment expenses	(7,400,000)		(5,300,000)		(14,400,000)		(10,200,000)
Other investment results	(1,200,000)		1,700,000		3,200,000		3,100,000
Net investment income	114,094,000		100,403,000		224,677,000		219,214,000
Homesite
Net Investment Income [Line Items]
Equity results			3,000,000	[1]			24,500,000	[1]
ORX
Net Investment Income [Line Items]
Equity results	(1,100,000)		(300,000)		(700,000)		400,000
Ares Management Limited Liability Company
Net Investment Income [Line Items]
Net investment income	3,000,000	[2]			3,100,000	[2]
Pillar Holdings and Funds | Pillar Capital Holdings Limited And Managed Funds
Net Investment Income [Line Items]
Equity results	$ 3,600,000	[2]	$ 2,700,000	[2]	$ 7,500,000	[2]	$ 4,300,000	[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.