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Schedule of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2016
Dec. 31, 2015
Pension Benefits        
Net Period Benefit Cost Assumptions [Line Items]        
Service cost $ 257 $ 234 $ 763 $ 702
Interest cost 941 935 2,823 2,805
Expected return on plan assets (548) (530) (1,645) (1,590)
Administrative expenses 2   6  
Amortization of prior service cost   9   27
Recognized actuarial (benefit) loss 446 567 1,338 1,701
Net periodic benefit cost 1,098 1,215 3,285 3,645
Other Benefits        
Net Period Benefit Cost Assumptions [Line Items]        
Service cost 20 41 60 191
Interest cost 50 103 150 524
Amortization of prior service cost (1,086) (899) (3,258) (1,920)
Recognized actuarial (benefit) loss (285) (281) (855) (770)
Net periodic benefit cost $ (1,301) $ (1,036) $ (3,903) $ (1,975)