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	Sep. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	$ 13,528	$ 32,980
Percent of Total Gross Unrealized Loss	100.00%
Fair Value Amount	972,572	934,607
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	836
Percent of Total Gross Unrealized Loss	6.00%
Fair Value Amount	11,737
Percent of Total Fair Value	1.00%
Due After One Year Through Five Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	4,374
Percent of Total Gross Unrealized Loss	32.00%
Fair Value Amount	370,199
Percent of Total Fair Value	38.00%
Due After Five Years Through Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	3,723
Percent of Total Gross Unrealized Loss	28.00%
Fair Value Amount	162,429
Percent of Total Fair Value	17.00%
Due After Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	992
Percent of Total Gross Unrealized Loss	7.00%
Fair Value Amount	102,724
Percent of Total Fair Value	11.00%
Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	3,603
Percent of Total Gross Unrealized Loss	27.00%
Fair Value Amount	$ 325,483
Percent of Total Fair Value	33.00%