Investments - Scheduled Maturities of Company's Fixed Maturity Securities Based on their Fair Values (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Losses, Total	$ 74,702	$ 86,000
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Gains, One year or less	1,779
Securities with Unrealized Gains, After one through five years	12,802
Securities with Unrealized Gains, After five through ten years	2,844
Securities with Unrealized Gains, After ten years	4,751
Securities with Unrealized Gains, No single maturity date	4,818
Securities with Unrealized Gains, Total	26,994
Securities with Unrealized Losses, One year or less	3,574
Securities with Unrealized Losses, After one through five years	17,345
Securities with Unrealized Losses, After five through ten years	30,879
Securities with Unrealized Losses, No single maturity date	21,267
Securities with Unrealized Losses, Total	73,065
All Fixed Maturity Securities, One year or less	5,353
All Fixed Maturity Securities, After one through five years	30,147
All Fixed Maturity Securities, After five through ten years	33,723
All Fixed Maturity Securities, After ten years	4,751
All Fixed Maturity Securities, No single maturity date	26,085
All Fixed Maturity Securities, Total	$ 100,059