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, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Pension Plans, Defined Benefit [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 115 $ 124 $ 231 $ 248
Interest cost 303 323 606 646
Expected return on assets (628) (665) (1,257) (1,329)
Amortization of actuarial loss 260 242 520 484
Net pension cost and postretirement benefit cost 50 24 100 49
Other Postretirement Benefit Plans [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 4 6 9 11
Amortization of actuarial loss 7 7 13 14
Net pension cost and postretirement benefit cost $ 11 $ 13 $ 22 $ 25