Amortized Cost and Estimated Fair Value of Fixed Maturity Available-for-Sale Securities by Contractual Maturities (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Amortized cost of fixed maturity AFS securities
Due in one year or less	$ 67,489	$ 56,748
Due after one year through five years	491,767	523,815
Due after five years through ten years	105,991	95,744
Due after ten years	501,814	485,720
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis, Total	1,167,061	1,162,027
Mortgage-backed securities and other asset-backed securities	187,336	221,760
Fixed maturity available-for-sale securities, amortized cost	1,354,397	1,383,787
Estimated fair value of fixed maturity AFS securities
Due in one year or less	68,442	57,489
Due after one year through five years	522,564	555,221
Due after five years through ten years	110,682	99,697
Due after ten years	569,354	549,354
Available-for-sale Securities, Debt Maturities, Single Maturity Date, Total	1,271,042	1,261,761
Mortgage-backed securities and other asset-backed securities	192,402	225,276
Total fixed maturity AFS securities	$ 1,463,444	$ 1,487,037