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 9 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2017
Dec. 31, 2016
Pension Plans, Defined Benefit [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 149 $ 151 $ 448 $ 451
Interest cost 356 362 1,067 1,087
Expected return on assets (743) (718) (2,232) (2,155)
Amortization of actuarial loss 253 337 760 1,013
Net pension cost and postretirement benefit cost 15 132 43 396
Other Postretirement Benefit Plans [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 6 5 19 19
Amortization of actuarial loss 9 11 28 30
Net pension cost and postretirement benefit cost $ 15 $ 16 $ 47 $ 49