Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value
Due in one year or less	$ 117,677
Due after one year through five years	576,742
Due after five years through ten years	462,171
Due after ten years	245,032
Mortgage- and asset-backed securities	606,184
Total	2,007,806	2,121,833
Amortized Cost
Due in one year or less	116,999
Due after one year through five years	566,164
Due after five years through ten years	461,911
Due after ten years	250,212
Mortgage- and asset-backed securities	593,221
Total	$ 1,988,507	$ 2,034,765