Scheduled Maturity Dates For Fixed Maturity Securities By Number Of Years Until Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Fair Value
Due in one year or less	$ 46,615
Due after one year through five years	627,418
Due after five years through ten years	385,720
Due after ten years	216,631
Mortgage- and asset-backed securities	667,179
Total	1,943,563	1,888,069
Amortized Cost
Due in one year or less	46,244
Due after one year through five years	611,661
Due after five years through ten years	363,151
Due after ten years	203,101
Mortgage- and asset-backed securities	638,919
Total	$ 1,863,076	$ 1,816,710