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Schedule of Net Periodic Benefit Cost (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Pension Plan and Supplemental Plan    
Net Period Benefit Cost Assumptions [Line Items]    
Service cost $ 234 $ 206
Interest cost 935 968
Expected return on plan assets (530) (685)
Amortization of prior service cost 9 12
Recognized actuarial benefit 567 247
Net periodic benefit cost 1,215 748
Other Benefits    
Net Period Benefit Cost Assumptions [Line Items]    
Service cost 75 68
Interest cost 211 226
Amortization of prior service cost (510) (508)
Recognized actuarial benefit (245) (325)
Net periodic benefit cost $ (469) $ (539)