Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets
Fixed maturity securities, available-for-sale, amortized cost (in dollars)	$ 9,638,404	$ 9,274,718
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	182,235,798	183,744,655
Common stock, shares outstanding	182,235,798	183,744,655
Accumulated other comprehensive income, tax provision (in dollars)	$ 135,344	$ 18,341
Deferred equity compensation, shares	320,193	181,818