Allowance for Credit Losses (Reserve Allowance for Various Credit Loss) (Details) $ in Thousands	6 Months Ended
	Sep. 30, 2020 USD ($)
Valuation And Qualifying Accounts [Abstract]
March 31, 2020	$ 3,684
Transition adjustment current expected credit losses	3,354
Write-offs against allowance	0
Recoveries	0
September 30, 2020	7,038
Trade Receivables
Valuation And Qualifying Accounts [Abstract]
March 31, 2020	2,680
Transition adjustment current expected credit losses	(411)
Write-offs against allowance	0
Recoveries	0
September 30, 2020	2,269
Investments, Fixed Maturities
Valuation And Qualifying Accounts [Abstract]
March 31, 2020	503
Transition adjustment current expected credit losses	3,755
Write-offs against allowance	0
Recoveries	0
September 30, 2020	4,258
Investments, Other
Valuation And Qualifying Accounts [Abstract]
March 31, 2020	501
Transition adjustment current expected credit losses	10
Write-offs against allowance	0
Recoveries	0
September 30, 2020	$ 511