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, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	$ 1,237	$ 10,782
Percent of Total Gross Unrealized Loss	100.00%
Fair Value Amount	91,169	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	25
Percent of Total Gross Unrealized Loss	2.00%
Fair Value Amount	11,387
Percent of Total Fair Value	12.00%
Due After One Year Through Five Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	112
Percent of Total Gross Unrealized Loss	9.00%
Fair Value Amount	19,473
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	27
Percent of Total Gross Unrealized Loss	2.00%
Fair Value Amount	5,532
Percent of Total Fair Value	6.00%
Due After Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	58
Percent of Total Gross Unrealized Loss	5.00%
Fair Value Amount	14,974
Percent of Total Fair Value	16.00%
Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	1,015
Percent of Total Gross Unrealized Loss	82.00%
Fair Value Amount	$ 39,803
Percent of Total Fair Value	45.00%