Investments - Scheduled Maturities of Company's Fixed Maturity Securities Based on their Fair Values (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Losses, Total	$ 21,699	$ 38,072
Fixed Maturities
Schedule of Available-for-sale Securities [Line Items]
Securities with Unrealized Gains, One year or less	9,422	8,791
Securities with Unrealized Gains, After one through five years	30,047	22,140
Securities with Unrealized Gains, After five through ten years	33,756	24,980
Securities with Unrealized Gains, After ten years	10,898	9,009
Securities with Unrealized Gains, No single maturity date	11,303	12,022
Securities with Unrealized Gains, Total	95,426	76,942
Securities with Unrealized Losses, After one through five years	5,801	12,888
Securities with Unrealized Losses, After five through ten years	15,594	21,450
Securities with Unrealized Losses, After ten years		1,742
Securities with Unrealized Losses, No single maturity date	304
Securities with Unrealized Losses, Total	21,699	36,080
All Fixed Maturity Securities, One year or less	9,422	8,791
All Fixed Maturity Securities, After one through five years	35,848	35,028
All Fixed Maturity Securities, After five through ten years	49,350	46,430
All Fixed Maturity Securities, After ten years	10,898	10,751
All Fixed Maturity Securities, No single maturity date	11,607	12,022
All Fixed Maturity Securities, Total	$ 117,125	$ 113,022