Accounting Pronouncements (Effects of Adoption of ASU 2018-12 Statement Of Operations) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Statements Adjusted [Abstract]
Benefits and losses	$ 45,344	$ 39,757
Amortization of deferred policy acquisition costs	8,045	7,672
Pretax earnings	338,695	445,399
Net earnings available to common shareholders	256,838	338,345
Common Stock [Member]
Statements Adjusted [Abstract]
Net earnings available to common shareholders	$ 0	$ 0
Basic and diluted earnings per share Common Stock	$ 1.27	$ 2.18
Nonvoting Common Stock [Member]
Statements Adjusted [Abstract]
Net earnings available to common shareholders	$ 0	$ 0
Basic and diluted earnings per share Common Stock	$ 1.31	$ 1.68
Operating Segments [Member] | Life Insurance [Member]
Statements Adjusted [Abstract]
Benefits and losses	$ 40,886	$ 35,378
Amortization of deferred policy acquisition costs	8,045	7,672
Pretax earnings	1,236	5,796
Net earnings available to common shareholders	$ 720	5,413
Previously Reported
Statements Adjusted [Abstract]
Benefits and losses		44,100
Pretax earnings		441,056
Net earnings available to common shareholders		$ 334,002
Previously Reported | Common Stock [Member]
Statements Adjusted [Abstract]
Basic and diluted earnings per share Common Stock		$ 2.15
Previously Reported | Nonvoting Common Stock [Member]
Statements Adjusted [Abstract]
Basic and diluted earnings per share Common Stock		$ 1.65
Effect of adoption
Statements Adjusted [Abstract]
Benefits and losses		$ (4,343)
Pretax earnings		4,343
Net earnings available to common shareholders		$ 4,343
Effect of adoption | Common Stock [Member]
Statements Adjusted [Abstract]
Basic and diluted earnings per share Common Stock		$ 0.03
Effect of adoption | Nonvoting Common Stock [Member]
Statements Adjusted [Abstract]
Basic and diluted earnings per share Common Stock		$ 0.03