Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Fair Value
Due in one year or less	$ 107,224
Due after one year through five years	801,129
Due after five years through ten years	356,251
Due after ten years	178,889
Mortgage- and asset-backed securities	678,340
Total	2,121,833	1,888,069
Amortized Cost
Due in one year or less	106,500
Due after one year through five years	780,715
Due after five years through ten years	333,257
Due after ten years	168,967
Mortgage- and asset-backed securities	645,326
Total	$ 2,034,765	$ 1,816,710