Quarterly report pursuant to Section 13 or 15(d)

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

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Employee Benefit Plans - Components of Postretirement Benefit Income and Pension Cost (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended 6 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Pension Plans, Defined Benefit [Member]
        
Defined Benefit Plan Disclosure [Line Items]        
Service cost $ 144 $ 136 $ 288 $ 272
Interest cost 339 356 679 713
Expected returns on assets (682) (685) (1,364) (1,369)
Amortization of unrecognized prior service cost (benefit) 1 1 2 2
Amortization of actuarial loss 251 254 501 506
Net pension cost and postretirement benefit income 53 62 106 124
Other Postretirement Benefit Plans [Member]
        
Defined Benefit Plan Disclosure [Line Items]        
Service cost            
Interest cost 8 10 16 19
Amortization of unrecognized prior service cost (benefit) (42) (42) (83) (83)
Amortization of actuarial loss 11 9 22 19
Net pension cost and postretirement benefit income $ (23) $ (23) $ (45) $ (45)