CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Fixed maturities, amortized cost	$ 5,357,436	$ 5,196,784
Cost	$ 3,991	$ 3,993
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	1,000,000,000	1,000,000,000
Common stock, shares issued (in shares)	371,353,000	371,353,000
Common stock, shares outstanding (in shares)	354,177,000	355,371,000
Treasury stock, shares at cost (in shares)	17,176,000	15,982,000