Reclassifications of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other than temporary impairment losses		$ 511	$ 3,217
Income taxes		37,422	58,550
Total reclassifications		1,400	(36,700)
Unrealized Appreciation of Investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications		1,400	(36,700)
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]	1,200	(59,600)
Other than temporary impairment losses		500	3,200
Income taxes		$ (300)	$ 19,700

[1] For the first three months of 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. See Note 3(g) of this Form 10-Q for additional information.