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Summary of Deferred Stock Unit Activity (Detail) - $ / shares
 12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2014
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Weighted-average Grant-Date Fair Value, Beginning Balance Outstanding $ 39.53 $ 48.68  
Weighted-average Grant-Date Fair Value, Dividend equivalents reinvested 13.36 34.63 $ 53.82
Weighted-average Grant-Date Fair Value, Retirement distribution 19.14 47.50 59.65
Weighted-average Grant-Date Fair Value, Granted 6.83 19.14 49.47
Weighted-average Grant-Date Fair Value, Ending Balance Outstanding $ 23.58 $ 39.53 $ 48.68
Number of Shares Beginning Balance Outstanding 185,060 146,388 144,007
Number of Shares, Dividend equivalents reinvested 15,064 3,794 2,492
Number of Shares, Retirement distribution (4,874) (21,492) (26,661)
Number of Shares, Granted 168,380 56,370 26,550
Number of Shares Ending Balance Outstanding 363,630 185,060 146,388