Net Investment Income (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Net Investment Income [Line Items]
Interest income		$ 102,500	$ 98,700	$ 201,700	$ 200,000
Dividend income		11,800	11,200	21,200	23,300
Investment expenses		(6,900)	(6,700)	(14,300)	(13,600)
Other investment results		3,700	(300)	9,400	(5,500)
Net investment income		101,656	106,860	217,194	211,723
Ares
Net Investment Income [Line Items]
Equity results	[1]	(12,600)	100	(7,400)	500
Pillar Holdings and Funds | Pillar Capital Holdings Limited And Managed Funds
Net Investment Income [Line Items]
Equity results	[1]	$ 3,200	$ 3,900	$ 6,600	$ 7,000

[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.