Accumulated Other Comprehensive Income Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020	$ 106,857
Foreign currency translation	(2,828)	$ (5,694)	$ 9,377
Unrealized net loss on investments	(62,626)	76,969	97,943
Change in fair value of cash flow hedges	457	(429)	(6,301)
Amounts reclassified into earnings on hedging activities	2,978	2,746	(2)
Change in postretirement benfit obligations	1,546	(1,387)	333
Other comprehensive income (loss)	(60,473)	72,205	101,350
Balance as of March 31, 2021	46,384	106,857
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020	(52,929)	(47,235)	(56,612)
Foreign currency translation	(2,828)	(5,694)	9,377
Unrealized net loss on investments	0	0	0
Change in fair value of cash flow hedges	0	0	0
Amounts reclassified into earnings on hedging activities	0	0	0
Change in postretirement benfit obligations	0	0	0
Other comprehensive income (loss)	(2,828)	(5,694)	9,377
Balance as of March 31, 2021	(55,757)	(52,929)	(47,235)
Unrealized Gain (Loss) on Investments
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020	167,653	90,684	(7,259)
Foreign currency translation	0	0	0
Unrealized net loss on investments	(62,626)	76,969	97,943
Change in fair value of cash flow hedges	0	0	0
Amounts reclassified into earnings on hedging activities	0	0	0
Change in postretirement benfit obligations	0	0	0
Other comprehensive income (loss)	(62,626)	76,969	97,943
Balance as of March 31, 2021	105,027	167,653	90,684
Fair Market Value of Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020	(3,879)	(6,196)	107
Foreign currency translation	0	0	0
Unrealized net loss on investments	0	0	0
Change in fair value of cash flow hedges	457	(429)	(6,301)
Amounts reclassified into earnings on hedging activities	2,978	2,746	(2)
Change in postretirement benfit obligations	0	0	0
Other comprehensive income (loss)	3,435	2,317	(6,303)
Balance as of March 31, 2021	(444)	(3,879)	(6,196)
Postretirement Benefit Obligation Gain (Loss)
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020	(3,988)	(2,601)	(2,934)
Foreign currency translation	0	0	0
Unrealized net loss on investments	0	0	0
Change in fair value of cash flow hedges	0	0	0
Amounts reclassified into earnings on hedging activities	0	0	0
Change in postretirement benfit obligations	1,546	(1,387)	333
Other comprehensive income (loss)	1,546	(1,387)	333
Balance as of March 31, 2021	(2,442)	(3,988)	(2,601)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) Components, Net of Tax [Roll Forward]
Balance as of March 31, 2020	106,857	34,652	(66,698)
Foreign currency translation	(2,828)	(5,694)	9,377
Unrealized net loss on investments	(62,626)	76,969	97,943
Change in fair value of cash flow hedges	457	(429)	(6,301)
Amounts reclassified into earnings on hedging activities	2,978	2,746	(2)
Change in postretirement benfit obligations	1,546	(1,387)	333
Other comprehensive income (loss)	(60,473)	72,205	101,350
Balance as of March 31, 2021	$ 46,384	$ 106,857	$ 34,652