Investments - Scheduled Maturities of Company's Fixed Maturity Securities Based on their Fair Values (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Losses, Total	$ 48,425	$ 38,072
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Gains, One year or less	11,067
Securities with Unrealized Gains, After one through five years	24,166
Securities with Unrealized Gains, After five through ten years	29,276
Securities with Unrealized Gains, After ten years	10,254
Securities with Unrealized Gains, No single maturity date	7,922
Securities with Unrealized Gains, Total	82,685
Securities with Unrealized Losses, After one through five years	8,770
Securities with Unrealized Losses, After five through ten years	30,152
Securities with Unrealized Losses, No single maturity date	194
Securities with Unrealized Losses, Total	39,116
Securities with No Unrealized Gains or Losses, After five through ten years	500
Securities with No Unrealized Gains or Losses, Total	500
All Fixed Maturity Securities, One year or less	11,067
All Fixed Maturity Securities, After one through five years	32,936
All Fixed Maturity Securities, After five through ten years	59,928
All Fixed Maturity Securities, After ten years	10,254
All Fixed Maturity Securities, No single maturity date	8,116
All Fixed Maturity Securities, Total	$ 122,301