Gross Unrealized Investment Losses (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fixed maturities
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	$ (10,782)	$ (20,762)
Less than 80% of amortized cost
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	(1,385)
Less than 80% of amortized cost | Fixed maturities
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	(1,039)
Less than 80% of amortized cost | Equity Securities
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	(346)
Less than 80% of amortized cost | Gross Unrealized Loss Position Up To Three Months
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	(243)
Less than 80% of amortized cost | Gross Unrealized Loss Position Up To Three Months | Equity Securities
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	(243)
Less than 80% of amortized cost | Gross Unrealized Loss Position Three To Six Months
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	(103)
Less than 80% of amortized cost | Gross Unrealized Loss Position Three To Six Months | Equity Securities
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	(103)
Less than 80% of amortized cost | > 12 months
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	(1,039)
Less than 80% of amortized cost | > 12 months | Fixed maturities
Gain (Loss) on Investments [Line Items]
Gross Unrealized Loss	$ (1,039)