Consolidated Balance Sheets Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Fixed maturity securities, allowance for credit loss	$ 20,739	$ 2,580
Fixed maturity securities, amortized cost	15,126,980	13,755,858
Cumulative effect adjustment resulting from changes in accounting principles	4,198	5,437
Cumulative effect adjustment resulting from changes in accounting principles	24,264	22,883
Reinsurance recoverable, allowance for credit loss	$ 7,373	$ 7,801
Preferred stock, par value (in dollars per share)	$ 0.10	$ 0.10
Preferred stock issued (in shares)	5,000,000	5,000,000
Preferred stock outstanding (in shares)	0	0
Common stock, par value (in dollar per share)	$ 0.20	$ 0.20
Common shares authorized (in shares)	500,000,000	500,000,000
Common shares issued (in shares)	177,372,943	177,825,150
Common shares outstanding (in shares)	177,372,943	177,825,150
Treasury stock issued at cost (in shares)	175,303,557	174,851,350