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	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	$ 18,719	$ 32,980
Percent of Total Gross Unrealized Loss	100.00%
Fair Value Amount	899,012	934,607
Percent of Total Fair Value	100.00%
Due in one year or less
Schedule of Available-for-sale Securities [Line Items]
Percent of Total Gross Unrealized Loss	0.00%
Fair Value Amount	1,701
Percent of Total Fair Value	0.00%
Due After One Year Through Five Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	1,697
Percent of Total Gross Unrealized Loss	9.00%
Fair Value Amount	316,024
Percent of Total Fair Value	35.00%
Due After Five Years Through Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	7,773
Percent of Total Gross Unrealized Loss	41.00%
Fair Value Amount	235,549
Percent of Total Fair Value	26.00%
Due After Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	4,753
Percent of Total Gross Unrealized Loss	26.00%
Fair Value Amount	140,210
Percent of Total Fair Value	16.00%
Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	4,496
Percent of Total Gross Unrealized Loss	24.00%
Fair Value Amount	$ 205,528
Percent of Total Fair Value	23.00%