Comprehensive Income (Loss) (Accumulated other comprehensive income (loss) components of net of tax) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020			$ 106,857
Foreign currency translation	$ 112	$ (2,566)	(2,288)	$ (5,193)
Unrealized net gain on investments	(11,992)	9,560	(43,637)	54,900
Change in fair value of cash flow hedges	178	26	71	(471)
Amount reclassified from AOCI	759	734	2,261	2,022
Other comprehensive income (loss)	(10,943)	7,754	(43,593)	51,258
Balance as of December 31, 2020	63,264		63,264
Foreign Currency Translation [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020			(52,929)
Foreign currency translation			(2,288)
Unrealized net gain on investments			0
Change in fair value of cash flow hedges			0
Amount reclassified from AOCI			0
Other comprehensive income (loss)			(2,288)
Balance as of December 31, 2020	(55,217)		(55,217)
Unrealized Net Gain on Investments [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020			167,653
Foreign currency translation			0
Unrealized net gain on investments			(43,637)
Change in fair value of cash flow hedges			0
Amount reclassified from AOCI			0
Other comprehensive income (loss)			(43,637)
Balance as of December 31, 2020	124,016		124,016
Fair Market Value of Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020			(3,879)
Foreign currency translation			0
Unrealized net gain on investments			0
Change in fair value of cash flow hedges			71
Amount reclassified from AOCI			2,261
Other comprehensive income (loss)			2,332
Balance as of December 31, 2020	(1,547)		(1,547)
Postretirement Benefit Obligation Gain [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020			(3,988)
Foreign currency translation			0
Unrealized net gain on investments			0
Change in fair value of cash flow hedges			0
Amount reclassified from AOCI			0
Other comprehensive income (loss)			0
Balance as of December 31, 2020	(3,988)		(3,988)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020			106,857
Foreign currency translation	112	(2,566)	(2,288)	(5,193)
Unrealized net gain on investments	(11,992)	9,560	(43,637)	54,900
Change in fair value of cash flow hedges	178	26	71	(471)
Amount reclassified from AOCI	759	$ 734	2,261	$ 2,022
Other comprehensive income (loss)			(43,593)
Balance as of December 31, 2020	$ 63,264		$ 63,264