Investments - Scheduled Maturities of Company's Fixed Maturity Securities Based on their Fair Values (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Losses, Total	$ 86,000	$ 57,573
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Gains, One year or less	2,302
Securities with Unrealized Gains, After one through five years	7,596
Securities with Unrealized Gains, After ten years	1,751
Securities with Unrealized Gains, No single maturity date	5,507
Securities with Unrealized Gains, Total	17,156
Securities with Unrealized Losses, One year or less	6,577
Securities with Unrealized Losses, After one through five years	23,015
Securities with Unrealized Losses, After five through ten years	33,098
Securities with Unrealized Losses, No single maturity date	21,743
Securities with Unrealized Losses, Total	84,433
All Fixed Maturity Securities, One year or less	8,879
All Fixed Maturity Securities, After one through five years	30,611
All Fixed Maturity Securities, After five through ten years	33,098
All Fixed Maturity Securities, After ten years	1,751
All Fixed Maturity Securities, No single maturity date	27,250
All Fixed Maturity Securities, Total	$ 101,589