Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans - Changes in Company's Benefit Obligation, Plan Assets and Funded Status for Plan (Detail)

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Employee Benefit Plans - Changes in Company's Benefit Obligation, Plan Assets and Funded Status for Plan (Detail) - USD ($)
$ in Thousands
12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2014
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation at beginning of year $ 39,052 $ 32,789  
Service cost 417 442  
Interest cost 1,437 1,434 $ 1,359
Actuarial loss (gain) (402) 5,573  
Benefit payments (1,350) (1,186)  
Liability released through annuity purchase (1,710)    
Projected benefit obligation at end of year 37,444 39,052 32,789
Change in fair value of plan assets      
Fair value of plan assets at beginning of year 40,384 38,548  
Employer contribution   55  
Actual return on plan assets (765) 2,967  
Benefit payments (1,350) (1,186)  
Annuities purchased (1,798)    
Fair value of plan assets at end of year 36,471 40,384 38,548
Funded status      
Funded status at end of year (973) 1,332  
Amount recognized in the Consolidated Balance Sheets (973) 1,332  
Other Postretirement Benefit Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation at beginning of year 968 951  
Interest cost 29 31 33
Actuarial loss (gain) (38) 75  
Benefit payments (84) (89)  
Projected benefit obligation at end of year 875 968 $ 951
Change in fair value of plan assets      
Employer contribution 84 89  
Benefit payments (84) (89)  
Funded status      
Funded status at end of year (875) (968)  
Amount recognized in the Consolidated Balance Sheets $ (875) $ (968)