Contractual Maturity by Number of Years Until Maturity for Fixed Maturity Securities with Gross Unrealized Loss (Detail) (Fixed maturities, USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	$ 1,261	$ 10,782
Percent of Total Gross Unrealized Loss	100.00%
Fair Value Amount	156,071	305,121
Percent of Total Fair Value	100.00%
Due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	7
Percent of Total Gross Unrealized Loss	1.00%
Fair Value Amount	8,560
Percent of Total Fair Value	5.00%
Due After One Year Through Five Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	62
Percent of Total Gross Unrealized Loss	5.00%
Fair Value Amount	33,336
Percent of Total Fair Value	21.00%
Due After Five Years Through Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	89
Percent of Total Gross Unrealized Loss	7.00%
Fair Value Amount	6,157
Percent of Total Fair Value	4.00%
Due After Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	283
Percent of Total Gross Unrealized Loss	22.00%
Fair Value Amount	28,901
Percent of Total Fair Value	19.00%
Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	820
Percent of Total Gross Unrealized Loss	65.00%
Fair Value Amount	$ 79,117
Percent of Total Fair Value	51.00%