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Schedule of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Pension Plan and Supplemental Plan    
Net Period Benefit Cost Assumptions [Line Items]    
Service cost $ 252 $ 234
Interest cost 941 935
Expected return on plan assets (548) (530)
Administrative expenses 2  
Amortization of prior service cost   9
Recognized actuarial (benefit) loss 446 567
Net periodic benefit cost 1,093 1,215
Other Benefits    
Net Period Benefit Cost Assumptions [Line Items]    
Service cost 20 75
Interest cost 50 211
Amortization of prior service cost (1,086) (510)
Recognized actuarial (benefit) loss (285) (245)
Net periodic benefit cost $ (1,301) $ (469)