Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Amortized cost on fixed maturities trading investments	$ 2,795,410	$ 2,804,275
Cost - equity security trading investments	331,770	313,528
Cost - short-term investments	$ 375,700	$ 185,353
Common Stock
Common stock, no par value (in dollars per share)	$ 0	$ 0
Common stock, shares authorized (in shares)	70,000,000	70,000,000
Common stock, shares issued (in shares)	55,289,000	55,164,000
Common stock, shares outstanding (in shares)	55,289,000	55,164,000