Investments - Schedule of Fixed Maturities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Fixed maturities available for sale, Amortized Cost - Due in one year or less	$ 102,473
Fixed maturities available for sale, Amortized Cost - Due from one to five years	494,066
Fixed maturities available for sale, Amortized Cost - Due from five to ten years	911,559
Fixed maturities available for sale, Amortized Cost - Due from ten to twenty years	3,109,054
Fixed maturities available for sale, Amortized Cost - Due after twenty years	7,766,780
Mortgage-backed and asset-backed securities, Amortized Cost	104,943
Total fixed maturities available for sale, Amortized Cost	12,488,875	11,963,406
Fixed maturities available for sale, Fair Value - Due in one year or less	104,065
Fixed maturities available for sale, Fair Value - Due from one to five years	538,995
Fixed maturities available for sale, Fair Value - Due from five to ten years	979,502
Fixed maturities available for sale, Fair Value - Due from ten to twenty years	3,303,084
Fixed maturities available for sale, Fair Value - Due after twenty years	7,853,621
Mortgage-backed and asset-backed securities, Fair Value	99,866
Debt Securities Fair Value	$ 12,879,133	$ 13,541,193