Consolidated Balance Sheets (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Investments:
Available for sale, amortized cost	$ 43,116,759	$ 39,953,955
Held for investment, fair value	$ 76,460	$ 68,766
Stockholders' equity:
Preferred stock, par value (dollars per share)	$ 1	$ 1
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (dollars per share)	$ 1	$ 1
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	89,331,087	88,001,130
Common stock, shares outstanding	89,331,087	88,001,130
Common stock, shares held in treasury	2,064,727	2,887,082