Accumulated Other Comprehensive Loss (Summary of Accumulated Other Comprehensive Income (Loss) Components, Net of Tax) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2025	Dec. 31, 2024
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Equity, Attributable to Parent, Beginning Balance			$ 7,498,143
Foreign currency translation	$ 1,841	$ 3,929	2,802	$ 3,712
Unrealized net gain on investments	20,026	54,108	59,460	44,663
Change in fair value of cash flow hedges	457	4,611	3,980	4,402
Amounts reclassified into earnings on hedging activities, Net	610	1,197	2,942	9,375
Other comprehensive income (loss)	21,714	53,593	61,224	35,978
Equity, Attributable to Parent, Ending Balance	7,743,809		7,743,809
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Equity, Attributable to Parent, Beginning Balance	(56,579)	(53,490)	(57,540)	(53,707)
Foreign currency translation	1,841	3,929	2,802	3,712
Other comprehensive income (loss)	1,841	3,929	2,802	3,712
Equity, Attributable to Parent, Ending Balance	(54,738)	(57,419)	(54,738)	(57,419)
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Equity, Attributable to Parent, Beginning Balance	(134,886)	(186,328)	(174,320)	(176,883)
Unrealized net gain on investments	20,026	54,108	59,460	44,663
Other comprehensive income (loss)	20,026	54,108	59,460	44,663
Equity, Attributable to Parent, Ending Balance	(114,860)	(132,220)	(114,860)	(132,220)
Fair Value of Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Equity, Attributable to Parent, Beginning Balance	(941)	(2,057)	(56)	6,330
Change in fair value of cash flow hedges	457	4,611	3,980	4,402
Amounts reclassified into earnings on hedging activities, Net	610	1,197	2,942	9,375
Other comprehensive income (loss)	153	3,414	1,038	4,973
Equity, Attributable to Parent, Ending Balance	(1,094)	1,357	(1,094)	1,357
Postretirement Benefit Obligation Gain [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Equity, Attributable to Parent, Beginning Balance	2,602	1,044	2,602	1,044
Equity, Attributable to Parent, Ending Balance	2,602	1,044	2,602	1,044
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Equity, Attributable to Parent, Beginning Balance	(189,804)	(240,831)	(229,314)	(223,216)
Foreign currency translation	1,841	3,929	2,802	3,712
Unrealized net gain on investments	20,026	54,108	59,460	44,663
Change in fair value of cash flow hedges	457	4,611	3,980	4,402
Amounts reclassified into earnings on hedging activities, Net	610	1,197	2,942	9,375
Other comprehensive income (loss)	21,714	53,593	61,224	35,978
Equity, Attributable to Parent, Ending Balance	$ (168,090)	$ (187,238)	$ (168,090)	$ (187,238)