Earnings Per Share Calculation Basic Diluted Earnings Per Share Voting Non Voting Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Earnings Per Share Diluted Other Disclosures [Abstract]
Net earnings available to common shareholders	$ 922,998	$ 1,123,286	$ 610,856
Voting Common Stock dividends declared	(19,608)	(29,412)	(49,019)
Non-Voting Common Stock dividends declared	$ (14,117)	$ 0	$ 0
Common Stock [Member]
Earnings Per Share Diluted Other Disclosures [Abstract]
Weighted Average Number Of Shares Outstanding Basic	19,607,788	19,607,788	19,607,788
Percent Weighted Average Shares Outstanding Common Stock	10.00%	10.00%	10.00%
Net earnings available to common shareholders	$ 0	$ 0	$ 0
Undistributed earnings available to common stockholders	889,273	1,093,874	561,837
Undistributed earnings available to common stockholders, participating securities	$ 88,927	$ 109,387	$ 56,184
Undistributed earnings per share, common stock	$ 4.54	$ 5.58	$ 2.87
Dividends declared per share, distributed	1.00	1.50	2.50
Basic and diluted earnings per share Common Stock	$ 5.54	$ 7.08	$ 5.37
Nonvoting Common Stock [Member]
Earnings Per Share Diluted Other Disclosures [Abstract]
Weighted Average Number Of Shares Outstanding Basic	176,470,092	176,470,092	176,470,092
Percent Weighted Average Shares Outstanding Common Stock	90.00%	90.00%	90.00%
Net earnings available to common shareholders	$ 0	$ 0	$ 0
Undistributed earnings available to common stockholders, participating securities	$ 800,346	$ 984,487	$ 505,653
Undistributed earnings per share, common stock	$ 4.54	$ 5.58	$ 2.87
Dividends declared per share, distributed	0.08	0	0
Basic and diluted earnings per share Common Stock	$ 4.62	$ 5.58	$ 2.87
Nonvoting Common Stock [Member] | Common Stock [Member]
Earnings Per Share Diluted Other Disclosures [Abstract]
Weighted Average Number Of Shares Outstanding Basic	196,077,880	196,077,880	196,077,880