Quarterly report pursuant to Section 13 or 15(d)

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

v3.10.0.1
Employee Benefit Plans - Components of Postretirement Benefit Cost and Pension Cost (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 143 $ 149
Interest cost 335 356
Expected return on assets (766) (744)
Amortization of actuarial loss 212 253
Net pension cost and postretirement benefit cost (76) 14
Other Postretirement Benefit Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Interest cost 6 6
Amortization of actuarial loss 7 10
Net pension cost and postretirement benefit cost $ 13 $ 16