Investments - Amortized Cost and Estimated Fair Values of Company's Fixed Maturity Investments Classified as Held-to-Maturity (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 790,866	$ 813,233
Gross Unrealized Gains	3,454	16,829
Gross Unrealized Losses Non-OTTI	(25,249)	(3,690)
Fair Value	769,071	826,372
U.S. Government and Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	19,771	20,257
Gross Unrealized Gains	8	322
Gross Unrealized Losses Non-OTTI	(458)	(20)
Fair Value	19,321	20,559
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	40,503	38,613
Gross Unrealized Gains	48	325
Gross Unrealized Losses Non-OTTI	(1,493)	(249)
Fair Value	39,058	38,689
Corporate
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	730,592	754,363
Gross Unrealized Gains	3,398	16,182
Gross Unrealized Losses Non-OTTI	(23,298)	(3,421)
Fair Value	$ 710,692	$ 767,124