Contractual Maturity by Number of Years Until Maturity for Fixed Maturity Securities with Gross Unrealized Loss (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	$ 1,304	$ 550
Fair Value Amount	19,928	10,925
Fixed maturities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	10,347	32,980
Percent of Total Gross Unrealized Loss	100.00%
Fair Value Amount	731,346	934,607
Percent of Total Fair Value	100.00%
Fixed maturities | Due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	2,638
Percent of Total Gross Unrealized Loss	25.00%
Fair Value Amount	21,919
Percent of Total Fair Value	3.00%
Fixed maturities | Due After One Year Through Five Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	3,791
Percent of Total Gross Unrealized Loss	37.00%
Fair Value Amount	334,046
Percent of Total Fair Value	46.00%
Fixed maturities | Due After Five Years Through Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	1,562
Percent of Total Gross Unrealized Loss	15.00%
Fair Value Amount	103,376
Percent of Total Fair Value	14.00%
Fixed maturities | Due After Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	158
Percent of Total Gross Unrealized Loss	2.00%
Fair Value Amount	21,533
Percent of Total Fair Value	3.00%
Fixed maturities | Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	2,198
Percent of Total Gross Unrealized Loss	21.00%
Fair Value Amount	$ 250,472
Percent of Total Fair Value	34.00%