Investments - Scheduled Maturities of Company's Fixed Maturity Securities Based on their Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Investments Debt And Equity Securities [Abstract]
Securities with Unrealized Gains, One year or less	$ 16,881	$ 9,380
Securities with Unrealized Gains, After one through five years	23,888	34,460
Securities with Unrealized Gains, After five through ten years	20,734	25,230
Securities with Unrealized Gains, After ten years	7,568	10,770
Securities with Unrealized Gains, No single maturity date	18,765	23,833
Securities with Unrealized Gains, Total	87,836	103,673
Securities with Unrealized Losses, One year or less
Securities with Unrealized Losses, After one through five years	12,937	11,518
Securities with Unrealized Losses, After five through ten years	20,194	15,181
Securities with Unrealized Losses, After ten years	3,051
Securities with Unrealized Losses, No single maturity date	8	336
Securities with Unrealized Losses, Total	36,190	27,035
Securities with No Unrealized Gains or Losses, One year or less	500	5
Securities with No Unrealized Gains or Losses, After one through five years
Securities with No Unrealized Gains or Losses, After five through ten years
Securities with No Unrealized Gains or Losses, After ten years
Securities with No Unrealized Gains or Losses, No single maturity date	212
Securities with No Unrealized Gains or Losses, Total	712	5
All Fixed Maturity Securities, One year or less	17,381	9,385
All Fixed Maturity Securities, After one through five years	36,825	45,978
All Fixed Maturity Securities, After five through ten years	40,928	40,411
All Fixed Maturity Securities, After ten years	10,619	10,770
All Fixed Maturity Securities, No single maturity date	18,985	24,169
All Fixed Maturity Securities, Total	$ 124,738	$ 130,713