Derivative Investments (Statements of Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Increase (decrease) in contract interest expense	$ 29,300	$ (15,700)
Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivatives	(38,976)	14,971
Derivatives not designated as hedging instruments | Equity index options | Investment Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivatives	(106,629)	42,003
Derivatives not designated as hedging instruments | Fixed-index products | Universal Life and Annuity Contract Interest
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivatives	$ 67,653	$ (27,032)