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, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Pension Plans, Defined Benefit [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 124 $ 143 $ 248 $ 286
Interest cost 323 335 646 670
Expected return on assets (665) (765) (1,329) (1,531)
Amortization of actuarial loss 242 211 484 423
Net pension cost and postretirement benefit cost 24 (76) 49 (152)
Other Postretirement Benefit Plans [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 6 6 11 12
Amortization of actuarial loss 7 7 14 14
Net pension cost and postretirement benefit cost $ 13 $ 13 $ 25 $ 26