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, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2023			$ 285,623
Foreign currency translation	$ 5,268	$ 215	2,888	$ 757
Unrealized net gain on investments	32,785	59,794	25,738	304,620
Change in fair value of cash flow hedges	4,352	115	2,823	6,532
Amount reclassified from AOCI	1,109	345	2,992	101
Other comprehensive income (loss)	32,978	60,239	23,019	298,744
Balance as of December 31, 2023	308,642		308,642
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2023	58,919	56,299	56,539	55,757
Foreign currency translation	5,268	215	2,888	757
Other comprehensive income (loss)	5,268	215	2,888	757
Balance as of December 31, 2023	53,651	56,514	53,651	56,514
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2023	225,693	191,175	232,740	53,651
Unrealized net gain on investments	32,785	59,794	25,738	304,620
Other comprehensive income (loss)	32,785	59,794	25,738	304,620
Balance as of December 31, 2023	258,478	250,969	258,478	250,969
Fair Market Value of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2023	9,299	6,419	4,007	444
Change in fair value of cash flow hedges	(4,352)	115	2,823	6,532
Amount reclassified from AOCI	(1,109)	345	2,992	101
Other comprehensive income (loss)	(5,461)	230	169	6,633
Balance as of December 31, 2023	3,838	6,189	3,838	6,189
Postretirement Benefit Obligation Gain [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2023	351	2,442	351	2,442
Balance as of December 31, 2023	351	2,442	351	2,442
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2023	275,664	243,497	285,623	4,992
Foreign currency translation	5,268	215	2,888	757
Unrealized net gain on investments	32,785	59,794	25,738	304,620
Change in fair value of cash flow hedges	4,352	115	2,823	6,532
Amount reclassified from AOCI	1,109	345	2,992	101
Other comprehensive income (loss)	(32,978)	60,239	23,019	298,744
Balance as of December 31, 2023	$ 308,642	$ 303,736	$ 308,642	$ 303,736