Amount of Gross Realized Capital Gains and Gross Realized Capital Losses of Available For Sale Securities (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Gain (Loss) on Investments [Line Items]
Gross realized capital gains	$ 46,200,000	$ 40,100,000	$ 153,900,000	$ 101,800,000
Gross realized capital losses	(4,700,000)	(13,100,000)	(15,500,000)	(23,900,000)
Net realized capital gains	$ 41,524,000	$ 26,977,000	$ 138,360,000	$ 77,879,000