Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value
Due in one year or less	$ 79,192
Due after one year through five years	616,576
Due after five years through ten years	458,136
Due after ten years	230,420
Mortgage- and asset-backed securities	597,407
Total	1,981,731	2,121,833
Amortized Cost
Due in one year or less	78,621
Due after one year through five years	603,165
Due after five years through ten years	455,826
Due after ten years	236,965
Mortgage- and asset-backed securities	583,857
Total	$ 1,958,434	$ 2,034,765