Provision for Taxes (Effective income tax rate reconciliation) (Details)	12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2017
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate	21.00%	31.55%	35.00%
Increase (Reduction) in Rate Resulting from [Abstract]
Deferred tax liability revaluation	0.00%	(58.25%)	0.00%
State taxes, net of federal benefit	2.41%	2.33%	2.66%
Foreign rate differential	0.15%	0.00%	(0.31%)
Federal tax credits	(0.15%)	(0.32%)	(0.41%)
Transition tax	(0.20%)	1.83%	0.00%
Dividends received deduction	(0.01%)	(0.03%)	(0.03%)
Phase III Tax	0.00%	0.63%	0.00%
Other	(0.86%)	(1.73%)	(0.32%)
Actual tax expense of operations	22.34%	(23.99%)	36.59%