Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value
Due in one year or less	$ 55,121
Due after one year through five years	756,593
Due after five years through ten years	326,731
Due after ten years	361,018
Mortgage- and asset-backed securities	845,762
Total	2,345,225	2,365,934
Amortized Cost
Due in one year or less	59,300
Due after one year through five years	746,400
Due after five years through ten years	315,462
Due after ten years	346,208
Mortgage- and asset-backed securities	827,393
Total	$ 2,294,763	$ 2,323,959