Net Investment Income (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net Investment Income [Line Items]
Interest income		$ 104,600	$ 99,000	$ 306,300	$ 299,000
Dividend income		6,700	12,200	27,900	35,500
Investment expenses		(5,800)	(6,200)	(20,100)	(19,800)
Other investment results		1,700	5,100	11,100	(400)
Net investment income		104,663	120,603	321,857	332,326
Ares
Net Investment Income [Line Items]
Equity results	[1]	6,900	4,600	(400)	5,100
Pillar Holdings and Funds | Pillar Capital Holdings Limited And Managed Funds
Net Investment Income [Line Items]
Equity results	[1]	$ (9,400)	$ 5,900	$ (2,900)	$ 12,900

[1] See Note 3(g) of this Form 10-Q for discussion of the Pillar Investments and the investment in Ares, each as defined therein.