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	2,380			2,380
Unrealized net gain (loss) on investments, net of tax	7,047			7,047
Change in fair value of cash flow hedges	7,175			7,175
Amounts reclassified into earnings on hedging activities, net	1,883			1,883
Net Income (Loss)	530,346				530,346			$ 530,346
Series N Non-Voting Common Stock dividends paid	(14,118)				(14,118)
Net activity	526,187			9,959	516,228
Balance, end of period at Sep. 30, 2023	7,030,378	10,497	453,643	275,664	7,519,376	525,653	151,997		176
Balance, beginning of period at Jun. 30, 2023	6,777,757	10,497	453,643	261,836	7,252,927	525,653	151,997		176
Cosolidated statement of change in equity
Foreign currency translation	2,849			2,849
Unrealized net gain (loss) on investments, net of tax	13,297			13,297
Change in fair value of cash flow hedges	3,333			3,333
Amounts reclassified into earnings on hedging activities, net	1,015			1,015
Net Income (Loss)	273,508				273,508			273,508
Series N Non-Voting Common Stock dividends paid	(7,059)				(7,059)
Net activity	252,621			13,828	266,449
Balance, end of period at Sep. 30, 2023	7,030,378	10,497	453,643	275,664	7,519,376	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	217			217
Unrealized net gain (loss) on investments, net of tax	9,445			9,445
Change in fair value of cash flow hedges	209			209
Amounts reclassified into earnings on hedging activities, net	8,178			8,178
Net Income (Loss)	382,215				382,215			382,215
Series N Non-Voting Common Stock dividends paid	(17,647)				(17,647)
Net activity	346,953			17,615	364,568
Balance, end of period at Sep. 30, 2024	7,519,398	10,497	462,548	240,831	7,964,658	525,653	151,997		176
Balance, beginning of period at Jun. 30, 2024	7,350,441	10,497	462,548	231,813	7,786,683	525,653	151,997		176
Cosolidated statement of change in equity
Foreign currency translation	421			421
Unrealized net gain (loss) on investments, net of tax	4,032			4,032
Change in fair value of cash flow hedges	1,696			1,696
Amounts reclassified into earnings on hedging activities, net	7,103			7,103
Net Income (Loss)	186,798				186,798			$ 186,798
Series N Non-Voting Common Stock dividends paid	(8,823)				(8,823)
Net activity	168,957			9,018	177,975
Balance, end of period at Sep. 30, 2024	$ 7,519,398	$ 10,497	$ 462,548	$ 240,831	$ 7,964,658	$ 525,653	$ 151,997		$ 176