Scheduled Maturity Dates for Fixed Maturity Securities by Number of Years Until Maturity (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value
Total	$ 2,967,909
Amortized Cost
Amortized Cost	2,997,997
Fixed Maturities
Fair Value
Due in one year or less	219,948
Due after one year through five years	722,278
Due after five years through ten years	336,352
Due after ten years	578,512
Mortgage-Backed and Asset-Backed Securities	1,104,451
Total	2,961,541	$ 3,057,054
Amortized Cost
Due in one year or less	221,066
Due after one year through five years	732,073
Due after five years through ten years	338,140
Due after ten years	578,504
Mortgage-Backed and Asset-Backed Securities	1,121,846
Amortized Cost	$ 2,991,629	$ 3,027,408