Defined Benefit Pension Plans - Schedule of Net Pension Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Contribution Pension And Other Postretirement Plans Disclosure [Abstract]
Employer service cost	$ 398	$ 341	$ 791	$ 685
Interest cost	27	10	54	20
Expected return on plan assets	(29)	(16)	(57)	(31)
Amortization of prior service credit	(3)		(7)
Amortization of net loss	47	43	93	87
Net pension cost for the year	$ 440	$ 378	$ 874	$ 761