Schedule of Net Periodic Benefit Cost for Postretirement Health Care and Life Insurance Plan (Detail) - Other Benefits - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2014
Net Period Benefit Cost Assumptions [Line Items]
Service cost	$ 212	$ 273	$ 405
Interest cost	584	904	1,048
Amortization of prior service cost	(2,996)	(2,032)	(2,032)
Recognized actuarial (gain)	(1,040)	(1,299)	(396)
Net periodic pension cost	$ (3,240)	$ (2,154)	$ (975)