Quarterly report pursuant to Section 13 or 15(d)

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

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Employee Benefit Plans - Components of Postretirement Benefit Cost and Pension Cost (Benefit) (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 150 $ 131
Interest cost 362 359
Expected return on assets (718) (795)
Amortization of actuarial loss 338 293
Net pension cost (benefit) and postretirement benefit cost 132 (12)
Other Postretirement Benefit Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost 6 7
Amortization of actuarial loss 10 10
Net pension cost (benefit) and postretirement benefit cost $ 16 $ 17