Net Investment Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Investment Income [Line Items]
Interest income		$ 376,400	$ 384,400	$ 348,000
Dividend income		54,000	63,000	59,600
Investment expenses		(27,200)	(28,800)	(20,300)
Other investment results		12,000	13,900	200
Net investment income		438,817	459,876	465,664
Ares
Net Investment Income [Line Items]
Equity results	[1]	6,600	8,600	9,100
ORX
Net Investment Income [Line Items]
Equity results		(6,300)	(3,200)	(1,000)
Homesite
Net Investment Income [Line Items]
Equity results	[2]			42,900
Pillar Holdings and Funds | Pillar Capital Holdings Limited And Managed Funds
Net Investment Income [Line Items]
Equity results	[1]	$ 23,300	$ 22,000	$ 27,200

[1] See Note 4(h) for discussion of the Pillar Investments and the investment in Ares as defined in Note 3.

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