Allowance for Credit Losses (Reserve Allowance for Various Credit Loss) (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Dec. 31, 2023	Mar. 31, 2023
Valuation And Qualifying Accounts [Abstract]
March 31, 2022	$ 6,407	$ 9,210
Transition adjustment current expected credit losses	459	(2,803)
Write-offs against allowance	0	0
Recoveries	0	0
December 31, 2023	6,866	6,407
Trade Receivables
Valuation And Qualifying Accounts [Abstract]
March 31, 2022	3,789	8,649
Transition adjustment current expected credit losses	556	(4,860)
Write-offs against allowance	0	0
Recoveries	0	0
December 31, 2023	4,345	3,789
Investments, Fixed Maturities
Valuation And Qualifying Accounts [Abstract]
March 31, 2022	2,101	60
Transition adjustment current expected credit losses	397	2,041
Write-offs against allowance	0	0
Recoveries	0	0
December 31, 2023	1,704	2,101
Investments, Other
Valuation And Qualifying Accounts [Abstract]
March 31, 2022	517	501
Transition adjustment current expected credit losses	300	16
Write-offs against allowance	0	0
Recoveries	0	0
December 31, 2023	$ 817	$ 517