Consolidated Balance Sheets Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Fixed maturity securities, allowance for credit loss	$ 2,567
Fixed maturity securities, amortized cost	13,536,264	$ 13,976,647
Cumulative effect adjustment resulting from changes in accounting principles	5,843	2,146
Cumulative effect adjustment resulting from changes in accounting principles	23,033	19,823
Reinsurance recoverable, allowance for credit loss	$ 7,741	$ 690
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)	750,000,000	750,000,000
Common shares issued (in shares)	178,217,537	183,411,907
Common shares outstanding (in shares)	178,217,537	183,411,907
Treasury stock issued at cost (in shares)	174,458,963	169,264,857