Condensed Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Less: Treasury Common Stock [Member]	Less: Treasury Preferred Stock [Member]	Nonvoting Common Stock [Member]	Nonvoting Common Stock [Member] Common Stock [Member]
Balance, beginning of period at Mar. 31, 2023	$ 6,504,191	$ 10,497	$ 453,643	$ 285,623	$ 7,003,148	$ 525,653	$ 151,997		$ 176
Cosolidated statement of change in equity
Foreign currency translation	2,888			2,888
Unrealized net gain (loss) on investments, net of tax	25,738			25,738
Change in fair value of cash flow hedges	2,823			2,823
Amounts reclassified into earnings on hedging activities, net	2,992			2,992
Net Income (Loss)	629,570				629,570			$ 629,570
Series N Non-Voting Common Stock dividends paid	(22,941)				(22,941)
Net activity	583,610			23,019	606,629
Balance, end of period at Dec. 31, 2023	7,087,801	10,497	453,643	308,642	7,609,777	525,653	151,997		176
Balance, beginning of period at Sep. 30, 2023	7,030,378	10,497	453,643	275,664	7,519,376	525,653	151,997		176
Cosolidated statement of change in equity
Foreign currency translation	5,268			5,268
Unrealized net gain (loss) on investments, net of tax	32,785			32,785
Change in fair value of cash flow hedges	4,352			4,352
Amounts reclassified into earnings on hedging activities, net	1,109			1,109
Net Income (Loss)	99,224				99,224			99,224
Series N Non-Voting Common Stock dividends paid	(8,823)				(8,823)
Net activity	57,423			32,978	90,401
Balance, end of period at Dec. 31, 2023	7,087,801	10,497	453,643	308,642	7,609,777	525,653	151,997		176
Balance, beginning of period at Mar. 31, 2024	7,172,445	10,497	462,548	223,216	7,600,090	525,653	151,997		176
Cosolidated statement of change in equity
Foreign currency translation	3,712			3,712
Unrealized net gain (loss) on investments, net of tax	44,663			44,663
Change in fair value of cash flow hedges	4,402			4,402
Amounts reclassified into earnings on hedging activities, net	9,375			9,375
Net Income (Loss)	449,381				449,381			449,381
Series N Non-Voting Common Stock dividends paid	(26,471)				(26,471)
Net activity	458,888			35,978	422,910
Balance, end of period at Dec. 31, 2024	7,631,333	10,497	462,548	187,238	8,023,000	525,653	151,997		176
Balance, beginning of period at Sep. 30, 2024	7,519,398	10,497	462,548	240,831	7,964,658	525,653	151,997		176
Cosolidated statement of change in equity
Foreign currency translation	3,929			3,929
Unrealized net gain (loss) on investments, net of tax	54,108			54,108
Change in fair value of cash flow hedges	4,611			4,611
Amounts reclassified into earnings on hedging activities, net	1,197			1,197
Net Income (Loss)	67,166				67,166			$ 67,166
Series N Non-Voting Common Stock dividends paid	(8,824)				(8,824)
Net activity	111,935			53,593	58,342
Balance, end of period at Dec. 31, 2024	$ 7,631,333	$ 10,497	$ 462,548	$ 187,238	$ 8,023,000	$ 525,653	$ 151,997		$ 176