Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Amortized cost on fixed maturities trading investments	$ 2,884,857	$ 2,795,410
Cost - equity security trading investments	388,408	331,770
Cost - short-term investments	260,697	375,700
Fixed assets, accumulated depreciation	$ 324,551	$ 319,429
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)	55,311,000	55,289,000
Common stock, shares outstanding (in shares)	55,311,000	55,289,000