Scheduled Maturity Dates For Fixed Maturity Securities By Number Of Years Until Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Fair Value
Due in one year or less	$ 80,858
Due after one year through five years	641,625
Due after five years through ten years	429,575
Due after ten years	229,037
Mortgage- and asset-backed securities	703,963
Total	2,085,058	1,888,069
Amortized Cost
Due in one year or less	80,272
Due after one year through five years	618,478
Due after five years through ten years	397,999
Due after ten years	211,295
Mortgage- and asset-backed securities	667,490
Total	$ 1,975,534	$ 1,816,710