Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Pension Plan and Supplemental Plan
Net Period Benefit Cost Assumptions [Line Items]
Service cost	$ 234	$ 206	$ 702	$ 618
Interest cost	935	968	2,805	2,904
Expected return on plan assets	(530)	(685)	(1,590)	(2,055)
Amortization of prior service cost	9	12	27	36
Recognized actuarial (benefit) loss	567	247	1,701	741
Net periodic benefit cost	1,215	748	3,645	2,244
Other Benefits
Net Period Benefit Cost Assumptions [Line Items]
Service cost	41	68	191	204
Interest cost	103	226	524	678
Amortization of prior service cost	(899)	(508)	(1,920)	(1,524)
Recognized actuarial (benefit) loss	(281)	(325)	(770)	(975)
Net periodic benefit cost	$ (1,036)	$ (539)	$ (1,975)	$ (1,617)