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Schedule of Carrying Value of Trust Assets, Including Unrealized Gains or Losses (Detail) - USD ($)
$ in Thousands
Jun. 30, 2017
Mar. 31, 2017
Compensation And Retirement Disclosure [Abstract]    
Investments held in Rabbi Trust $ 8,723 $ 8,759
Unrealized losses in fair value of trust assets (9) (95)
Unrealized losses in fair value of trust assets are net of income tax expense of (223) (223)
Obligations under the supplemental plan $ 29,701 $ 29,108