Employee Benefit Plans - Components of Postretirement Benefit Expense (Income) and Pension Cost (Benefit) (Detail) - Other Postretirement Benefit Plans [Member] - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Interest cost on accumulated benefit obligation	$ 18	$ 22	$ 25
Amortization of actuarial loss	27	28	28
Net pension (benefit) cost and postretirement benefit expense	$ 45	$ 50	$ 53