Net Investment Income (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net Investment Income [Line Items]
Interest income		$ 104,800	$ 102,500	$ 206,800	$ 201,700
Dividend income		22,300	11,800	38,600	21,200
Investment expenses		(6,600)	(6,900)	(18,600)	(14,300)
Other investment results		4,600	3,700	8,500	9,400
Net investment income		126,273	101,656	250,399	217,194
Limited partnership interests in certain subsidiaries of Ares
Net Investment Income [Line Items]
Equity results	[1]	(700)	(12,600)	13,200	(7,400)
Pillar Capital Holdings Limited And Managed Funds
Net Investment Income [Line Items]
Equity results	[1]	$ 1,900	$ 3,200	$ 1,900	$ 6,600

[1] See Note 3(h) of this Form 10-Q for discussion of the Pillar Investments, as defined therein, and limited partnership interests in certain subsidiaries of Ares.