Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Equity securities, cost	$ 1,661,468	$ 1,436,540
Debt securities, amortized cost	$ 14,942,612	$ 15,593,278
Common stock, shares authorized	22,000,000	22,000,000
Common stock, shares issued	17,459,961	17,478,746
Treasury stock, shares	693,769	588,123