Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value
Due in one year or less	$ 109,496
Due after one year through five years	636,433
Due after five years through ten years	480,898
Due after ten years	237,966
Mortgage- and asset-backed securities	613,210
Total	2,078,003	2,121,833
Amortized Cost
Due in one year or less	108,751
Due after one year through five years	616,510
Due after five years through ten years	459,528
Due after ten years	230,326
Mortgage- and asset-backed securities	586,750
Total	$ 2,001,865	$ 2,034,765