Consolidated Balance Sheets Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Fixed maturity securities, allowance for credit loss	$ 67,463
Debt Securities, Available-for-sale and Held-to-maturity, Amortized Cost	13,818,447	$ 13,976,647
Cumulative effect adjustment resulting from changes in accounting principles	3,928	2,146
Cumulative effect adjustment resulting from changes in accounting principles	21,524	19,823
Reinsurance recoverable, allowance for credit loss	$ 6,800	$ 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)	$ 0.2	$ 0.2
Common shares authorized (in shares)	500,000,000	500,000,000
Common shares issued (in shares)	179,836,714	183,411,907
Common shares outstanding (in shares)	179,836,714	183,411,907
Treasury stock issued at cost (in shares)	172,840,050	169,264,857