Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair Value
Due in one year or less	$ 65,454
Due after one year through five years	551,225
Due after five years through ten years	372,275
Due after ten years	215,139
Mortgage- and asset-backed securities	683,976
Total	1,888,069	1,882,245
Amortized Cost
Due in one year or less	64,925
Due after one year through five years	542,238
Due after five years through ten years	349,061
Due after ten years	201,523
Mortgage- and asset-backed securities	658,963
Total	$ 1,816,710	$ 1,855,598