Investments - Scheduled Maturities of Company's Fixed Maturity Securities Based on their Fair Values (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Losses, Total	$ 47,996	$ 57,573
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Gains, One year or less	4,821
Securities with Unrealized Gains, After one through five years	24,019
Securities with Unrealized Gains, After five through ten years	16,149
Securities with Unrealized Gains, After ten years	7,762
Securities with Unrealized Gains, No single maturity date	5,709
Securities with Unrealized Gains, Total	58,460
Securities with Unrealized Losses, One year or less	3,572
Securities with Unrealized Losses, After one through five years	2,112
Securities with Unrealized Losses, After five through ten years	12,957
Securities with Unrealized Losses, After ten years	4,958
Securities with Unrealized Losses, No single maturity date	22,892
Securities with Unrealized Losses, Total	46,491
Securities with No Unrealized Gains or Losses, After one through five years	2,000
Securities with No Unrealized Gains or Losses, Total	2,000
All Fixed Maturity Securities, One year or less	8,393
All Fixed Maturity Securities, After one through five years	28,131
All Fixed Maturity Securities, After five through ten years	29,106
All Fixed Maturity Securities, After ten years	12,720
All Fixed Maturity Securities, No single maturity date	28,601
All Fixed Maturity Securities, Total	$ 106,951