Net Investment Gains (Losses) (Net Investment Gains (Losses)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Realized and Unrealized Investment Gains Losses [Line Items]
Fixed maturity securities, Gains	$ 27,819	$ 23,900	$ 26,752
Fixed maturity securities, losses	(56,096)	(13,636)	(13,733)
Net realized gains on investment sales	32,647	23,306	435,150
Change in unrealized (losses) gains	(25,868)	85,292	(320,413)
Investment funds	31,481	(2,825)	(212)
Real estate (2)	101,554	5,965	27,816
Loans receivable	0	(970)	2,838
Other	(38,023)	(329)	1,977
Net realized and unrealized gains on investments in earnings before allowance for expected credit losses	73,514	120,703	160,175
Fixed maturity securities	33,134	0	(5,687)
Loans receivable	(3,648)	0	0
Change in allowance for expected credit losses on investments	29,486	0	(5,687)
Net investment gains	103,000	120,703	154,488
Income tax expense	(21,630)	(25,348)	(32,442)
After-tax net investment gains	81,370	$ 95,355	$ 122,046
New York City Complex
Realized and Unrealized Investment Gains Losses [Line Items]
Real estate (2)	$ 105,000