Provision for Taxes (Effective income tax rate reconciliation) (Details)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate	31.55%	35.00%	35.00%
Increase (Reduction) in Rate Resulting from [Abstract]
Deferred tax liability revaluation	(58.25%)	0.00%	0.00%
State taxes, net of federal benefit	2.33%	2.66%	2.34%
Foreign rate differential	0.00%	(0.31%)	(0.24%)
Federal tax credits	(0.32%)	(0.41%)	(0.19%)
Transition tax	1.83%	0.00%	0.00%
Dividends received deduction	(0.03%)	(0.03%)	(0.02%)
Phase III Tax	0.63%	0.00%	0.00%
Other	(1.73%)	(0.32%)	(0.49%)
Actual tax expense of operations	(23.99%)	36.59%	36.40%