Provision for Taxes (Effective income tax rate reconciliation) (Details)	12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate	21.00%	21.00%	21.00%
Increase (Reduction) in Rate Resulting from [Abstract]
State taxes, net of federal benefit	3.56%	3.24%	2.53%
Foreign rate differential	0.08%	0.05%	0.00%
Federal tax credits	0.48%	0.19%	0.99%
Tax-exempt income	0.08%	0.03%	0.08%
Dividend received deduction	0.01%	0.00%	0.01%
Other	0.15%	(0.20%)	0.87%
Actual tax expense of operations	24.22%	23.87%	23.32%