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, 2024	Mar. 31, 2023	Mar. 31, 2022
Earnings Per Share Diluted Other Disclosures [Abstract]
Net earnings available to common shareholders	$ 628,707	$ 924,472	$ 1,124,362
Undistributed earnings available to common stockholders	$ 596,942	$ 890,747	$ 1,094,950
Basic earnings per share Common Stock	$ 3.04
Diluted earnings per share Common Stock	$ 3.04
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
Voting Common Stock dividends declared	0	(19,608)	(29,412)
Non-Voting Common Stock dividends declared	(31,765)	(14,117)	0
Undistributed earnings available to common stockholders	$ 59,694
Undistributed earnings available to common stockholders, participating securities		$ 89,075	$ 109,495
Undistributed earnings per share, common stock	$ 3.04	$ 4.54	$ 5.58
Dividends declared per share, distributed	0	1	1.5
Basic earnings per share Common Stock	$ 3.04	5.54	7.08
Diluted earnings per share Common Stock		$ 5.54	$ 7.08
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
Voting Common Stock dividends declared	0	(19,608)	(29,412)
Non-Voting Common Stock dividends declared	(31,765)	(14,117)	0
Undistributed earnings available to common stockholders, participating securities	$ 537,248	$ 801,672	$ 985,455
Undistributed earnings per share, common stock	$ 3.04	$ 4.54	$ 5.58
Dividends declared per share, distributed	0.18	0.08
Basic earnings per share Common Stock	3.22	4.62	5.58
Diluted earnings per share Common Stock	$ 3.22	$ 4.62	$ 5.58
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