Quarterly report pursuant to Section 13 or 15(d)

Employee Benefit Plans - Components of Postretirement Benefit Cost and Pension Cost (Detail)

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Employee Benefit Plans - Components of Postretirement Benefit Cost and Pension Cost (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Pension Plans, Defined Benefit [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 143 $ 150 $ 286 $ 299
Interest cost 335 355 670 711
Expected return on assets (765) (745) (1,531) (1,489)
Amortization of actuarial loss 211 254 423 507
Net pension (income) cost and postretirement benefit cost (76) 14 (152) 28
Other Postretirement Benefit Plans [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 6 7 12 13
Amortization of actuarial loss 7 9 14 19
Net pension (income) cost and postretirement benefit cost $ 13 $ 16 $ 26 $ 32