Schedule of Assumptions Used in Net Periodic Benefit Cost and Benefit Obligations (Detail)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Compensation And Retirement Disclosure [Abstract]
Net Periodic Benefit Costs - Discount Rate	4.03%	3.83%	3.70%
Net Periodic Benefit Costs - Expected Return on Plan Assets	7.50%	7.50%	8.00%
Net Periodic Benefit Costs - Rate of Compensation Increase	3.50%	3.50%	3.50%
Benefit Obligations - Discount Rate	4.12%	4.03%
Benefit Obligations - Rate of Compensation Increase	3.50%	3.50%