Investments (Changes in Net Unrealized Gains/Losses on Investments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Investments [Abstract]
Fixed maturity securities available for sale carried at fair value	$ (2,862,408)	$ 1,517,520
Adjustment for effect on other balance sheet accounts:
Deferred policy acquisition costs and deferred sales inducements	1,244,753	(800,901)
Deferred income tax asset/liability	339,708	(150,490)
Total adjustment for effect on other balance sheet accounts	1,584,461	(951,391)
Change in net unrealized gains/losses on investments carried at fair value	$ (1,277,947)	$ 566,129