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Treasury Stock - Summary of Share Repurchases and Cumulatively Since Inception of Authorization (Detail) - USD ($)
12 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Mar. 31, 2016
Equity [Abstract]      
Shares repurchased 249,245 745,575 893,771
Cost $ 11,187,000 $ 27,999,000 $ 31,525,000
Average price $ 44.88 $ 37.56 $ 35.27
Shares repurchased, Cumulative 34,881,079 34,631,834  
Cost, Cumulative $ 430,989,000 $ 419,802,000  
Average price, Cumulative $ 12.36