Accounting Pronouncements (Adoption Of New Accounting Pronouncement Adjustments To Select Tables) (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022
Statements Adjusted [Abstract]
Assets	$ 18,100,734		$ 19,002,576		$ 18,090,124
Liabilities	11,596,543		11,914,775
Stockholders Equity Including Portion Attributable To Noncontrolling Interest	6,504,191	$ 5,894,075	$ 7,087,801	$ 7,030,378	$ 6,455,727	$ 6,324,173
Scenario Previously Reported [Member]
Statements Adjusted [Abstract]
Assets	18,124,648	17,299,581
Liabilities	11,596,313	11,347,089
Stockholders Equity Including Portion Attributable To Noncontrolling Interest	6,528,335	5,952,492
Cumulative Effect Period Of Adoption Adjustment [Member] | Life And Annuity Insurance Product Line [Member]
Statements Adjusted [Abstract]
Derecognition of shadow reserves	(25,141)	26,131
Re-measurement due to discount rate	0	0
Other adjustments	1,227	1,471
Subtotal	(23,914)	27,602
After adoption	18,100,734	17,327,183
Cumulative Effect Of Adoption Liabilities [Member] | Life And Annuity Insurance Product Line [Member]
Statements Adjusted [Abstract]
Derecognition of FIT on shadow reserves	(5,280)	5,488
Re-measurement due to discount rate	(1,626)	87,258
Re-measurement due to discount rate FIT	342	(18,324)
Other adjustments	6,794	8,511
Subtotal	230	82,933
After adoption	11,596,543	11,430,022
Cumulative Effect Of Adoption Comprehensive Income [Member]
Statements Adjusted [Abstract]
Stockholders Equity Including Portion Attributable To Noncontrolling Interest	267,046	46,384
Cumulative Effect Of Adoption Comprehensive Income [Member] | Life And Annuity Insurance Product Line [Member]
Statements Adjusted [Abstract]
Derecognition of FIT on shadow reserves	19,861	20,644
Re-measurement due to discount rate	1,626	87,258
Re-measurement due to discount rate FIT	342	18,324
Other adjustments	0	0
Subtotal	18,577	48,290
After adoption	285,623	1,906
Cumulative Effect Of Adoption Stockholders Equity [Member] | Life And Annuity Insurance Product Line [Member]
Statements Adjusted [Abstract]
Derecognition of shadow reserves	19,861	20,644
Re-measurement due to discount rate FIT	1,284	68,934
Other adjustments	5,567	7,042
Subtotal	24,144	55,332
After adoption	$ 6,504,191	$ 5,897,160