Investments - Unrealized Gain (Loss) on Investments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Gain (Loss) on Investments [Line Items]
Net change in unrealized gains (losses)	$ (1,166,032)	$ 1,283,062	$ (1,183,652)
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Net change in unrealized gains (losses)	(1,163,295)	1,279,190	(1,187,529)
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Net change in unrealized gains (losses)	158	(308)	317
Securities [Member]
Gain (Loss) on Investments [Line Items]
Net change in unrealized gains (losses)	(1,163,137)	1,278,882	(1,187,212)
Other Investments [Member]
Gain (Loss) on Investments [Line Items]
Net change in unrealized gains (losses)	$ (2,895)	$ 4,180	$ 3,560