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
Jun. 30, 2019
Jun. 30, 2018
Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 124 $ 143
Interest cost 323 335
Expected return on assets (664) (766)
Amortization of actuarial loss 242 212
Net pension cost and postretirement benefit cost 25 (76)
Other Postretirement Benefit Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost 5 6
Amortization of actuarial loss 7 7
Net pension cost and postretirement benefit cost $ 12 $ 13