CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Fixed income, amortized cost	$ 6,397,658	$ 6,317,164
Equity securities, cost	$ 15,838	$ 17,522
Shareholders' equity:
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)	320,336,000	338,573,000
Treasury stock, shares at cost (in shares)	51,017,000	32,779,000