Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Fixed maturities, available for sale, amortized cost	$ 14,188,050	$ 13,251,871
Long-term debt, fair value	$ 1,233,019	$ 856,291
Preferred stock, par value	$ 1	$ 1
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	320,000,000	320,000,000
Common stock, shares issued	127,218,183	130,218,183
Common stock, shares held in treasury	9,187,075	7,848,231