Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Fixed maturity securities available for sale, amortized cost	$ 9,470,795	$ 10,048,100
Equity securities available for sale, cost	$ 450,563	$ 434,875
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	800,000,000	800,000,000
Common stock, shares outstanding (in shares)	65,850,386	69,299,559	71,828,208	78,664,029
Treasury stock, at cost (in shares)	83,523,031	79,338,142