Provision for Taxes (Effective income tax rate reconciliation) (Details)	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax rate	35.00%	35.00%	35.00%
Increase (Reduction) in Rate Resulting from [Abstract]
State taxes, net of federal benefit	2.66%	2.34%	2.21%
Foreign rate differential	(0.31%)	(0.24%)	(0.32%)
Federal tax credits	(0.41%)	(0.19%)	(0.29%)
Dividends received deduction	(0.03%)	(0.02%)	(0.03%)
Other	(0.32%)	(0.49%)	(0.11%)
Actual tax expense of operations	36.59%	36.40%	36.46%