Derivative Investments (Statements of Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Increase (decrease) in contract interest expense	$ 3,700	$ (6,800)	$ 29,300	$ (27,100)
Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivatives	(2,599)	6,829	(25,121)	26,190
Derivatives not designated as hedging instruments | Equity index options | Net investment income (loss)
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivatives	31,520	3,296	(34,865)	63,127
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	$ (34,119)	$ 3,533	$ 9,744	$ (36,937)