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, 2017
Mar. 31, 2016
Mar. 31, 2015
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation at beginning of year $ 37,444 $ 39,052  
Service cost 496 417  
Interest cost 1,450 1,437 $ 1,434
Actuarial gain (994) (402)  
Benefit payments (1,818) (1,350)  
Liability released through annuity purchase (1,118) (1,710)  
Projected benefit obligation at end of year 35,460 37,444 39,052
Change in fair value of plan assets      
Fair value of plan assets at beginning of year 36,471 40,384  
Actual return on plan assets 4,393 (765)  
Benefit payments (1,818) (1,350)  
Annuities purchased (1,246) (1,798)  
Fair value of plan assets at end of year 37,800 36,471 40,384
Funded status      
Funded status at end of year 2,340 (973)  
Amount recognized in the Consolidated Balance Sheets 2,340 (973)  
Other Postretirement Benefit Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation at beginning of year 875 968  
Interest cost 26 29 31
Actuarial gain 20 (38)  
Benefit payments (77) (84)  
Projected benefit obligation at end of year 844 875 $ 968
Change in fair value of plan assets      
Employer contribution 77 84  
Benefit payments (77) (84)  
Funded status      
Funded status at end of year (844) (875)  
Amount recognized in the Consolidated Balance Sheets $ (844) $ (875)