Quarterly report pursuant to Section 13 or 15(d)

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

v3.5.0.2
Employee Benefit Plans - Components of Postretirement Benefit Cost and Pension Cost (Benefit) (Detail) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Pension Plans, Defined Benefit [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 150 $ 130 $ 300 $ 261
Interest cost 363 359 725 718
Expected return on assets (719) (795) (1,437) (1,590)
Amortization of actuarial loss 338 294 676 587
Net pension cost (benefit) and postretirement benefit cost 132 (12) 264 (24)
Other Postretirement Benefit Plans [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Interest cost 8 6 14 13
Amortization of actuarial loss 9 10 19 20
Net pension cost (benefit) and postretirement benefit cost $ 17 $ 16 $ 33 $ 33