Reclassifications of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains		$ 6,551	$ 3,241	$ (107,222)
Other than temporary impairment losses		19,660	1,328
Income taxes		233,435	(15,062)	$ (63,802)
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		(20,400)	11,700
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized capital gains	[1]	(45,500)	13,500
Other than temporary impairment losses		19,700	1,300
Income taxes		$ 5,400	$ (3,100)

[1] For 2019, excludes a $38.4 million pre-tax loss on the Put Option and a $13.6 million pre-tax loss from the December 2019 sale of a privately held investment accounted for under the equity method. For 2018, excludes a $45.7 million pre-tax gain from AIHL’s conversion of its limited partnership interests in certain subsidiaries of Ares into Ares common units, and a $35.4 million capital loss due to an impairment charge from the write-down of certain SORC assets arising from a decline in energy prices as of December 31, 2018. See Note 4 for additional information.