Reclassifications of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains	$ 41,524	$ 26,977	$ 138,360	$ 77,879
Other than temporary impairment losses	(932)	(8,908)	(6,152)	(41,220)
Income taxes	(53,186)	(33,282)	(116,868)	(90,377)
Net earnings	149,234	113,709	353,875	310,003
Reclassification out of Accumulated Other Comprehensive Income | Unrealized Appreciation of Investments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net realized capital gains	(41,500)	(27,000)	(138,400)	(77,900)
Other than temporary impairment losses	900	8,900	6,200	41,200
Income taxes	14,200	6,300	46,300	12,800
Net earnings	$ (26,400)	$ (11,800)	$ (85,900)	$ (23,900)