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, 2018
Mar. 31, 2017
Mar. 31, 2016
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation at beginning of year $ 35,460 $ 37,444  
Service cost 494 496  
Interest cost 1,423 1,450 $ 1,437
Actuarial gain (44) (994)  
Benefit payments (2,002) (1,818)  
Liability released through annuity purchase (890) (1,118)  
Projected benefit obligation at end of year 34,441 35,460 37,444
Change in fair value of plan assets      
Fair value of plan assets at beginning of year 37,800 36,471  
Employer contribution 52    
Actual return on plan assets 3,958 4,393  
Benefit payments (2,002) (1,818)  
Annuities purchased (998) (1,246)  
Fair value of plan assets at end of year 38,810 37,800 36,471
Funded status      
Funded status at end of year 4,369 2,340  
Amount recognized in the Consolidated Balance Sheets 4,369 2,340  
Other Postretirement Benefit Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation at beginning of year 844 875  
Interest cost 26 26 29
Actuarial gain (73) 20  
Benefit payments (74) (77)  
Projected benefit obligation at end of year 723 844 $ 875
Change in fair value of plan assets      
Employer contribution 74 77  
Benefit payments (74) (77)  
Funded status      
Funded status at end of year (723) (844)  
Amount recognized in the Consolidated Balance Sheets $ (723) $ (844)