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, 2019
Mar. 31, 2018
Mar. 31, 2017
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation at beginning of year $ 34,441 $ 35,460  
Service cost 468 494  
Interest cost 1,339 1,423 $ 1,450
Actuarial loss (gain) 462 (44)  
Benefit payments (972) (2,002)  
Liability released through annuity purchase (1,589) (890)  
Projected benefit obligation at end of year 34,149 34,441 35,460
Change in fair value of plan assets      
Fair value of plan assets at beginning of year 38,810 37,800  
Employer contribution 30 52  
Actual return on plan assets 2,266 3,958  
Benefit payments (972) (2,002)  
Annuities purchased (1,718) (998)  
Fair value of plan assets at end of year 38,416 38,810 37,800
Funded status      
Funded status at end of year 4,267 4,369  
Amount recognized in the Consolidated Balance Sheets 4,267 4,369  
Other Postretirement Benefit Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligation at beginning of year 723 844  
Interest cost 25 26 26
Actuarial loss (gain) 2 (73)  
Benefit payments (68) (74)  
Projected benefit obligation at end of year 682 723 $ 844
Change in fair value of plan assets      
Employer contribution 68 74  
Benefit payments (68) (74)  
Funded status      
Funded status at end of year (682) (723)  
Amount recognized in the Consolidated Balance Sheets $ (682) $ (723)