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	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	$ 2,837	$ 10,782
Percent of Total Gross Unrealized Loss	100.00%
Fair Value Amount	187,488	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	108
Percent of Total Gross Unrealized Loss	4.00%
Fair Value Amount	11,872
Percent of Total Fair Value	6.00%
Due after one year through five years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	530
Percent of Total Gross Unrealized Loss	19.00%
Fair Value Amount	77,548
Percent of Total Fair Value	41.00%
Due after five years through ten years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	305
Percent of Total Gross Unrealized Loss	11.00%
Fair Value Amount	33,587
Percent of Total Fair Value	18.00%
Due After Ten Years
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	111
Percent of Total Gross Unrealized Loss	4.00%
Fair Value Amount	12,478
Percent of Total Fair Value	7.00%
Mortgage- and asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Gross Unrealized Loss Amount	1,783
Percent of Total Gross Unrealized Loss	62.00%
Fair Value Amount	$ 52,003
Percent of Total Fair Value	28.00%