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, 2017
Jun. 30, 2016
Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 149 $ 150
Interest cost 356 362
Expected return on assets (744) (718)
Amortization of actuarial loss 253 338
Net pension cost and postretirement benefit cost 14 132
Other Postretirement Benefit Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost 6 6
Amortization of actuarial loss 10 10
Net pension cost and postretirement benefit cost $ 16 $ 16