Consolidated Balance Sheets (unaudited) (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Fixed maturity securities available for sale, amortized cost	$ 8,709,444	$ 9,470,795
Equity securities available for sale, cost	$ 382,168	$ 450,563
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)	60,612,310	65,850,386
Treasury stock, at cost (in shares)	89,263,289	83,523,031