Derivative Investments (Statements of Earnings) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments, Gain (Loss) [Line Items]
Increase (decrease) in contract interest expense	$ (3,700)	$ (4,700)	$ 25,600	$ (20,300)
Derivatives not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Income on Derivatives	16,453	4,389	(22,521)	19,360
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	40,243	17,828	(66,386)	59,830
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	$ (23,790)	$ (13,439)	$ 43,865	$ (40,470)