Capital Management and Dividends - Additional Information (Detail) $ / shares in Units, $ / shares in Units, $ in Millions, $ in Millions  | 
2 Months Ended | 3 Months Ended | 12 Months Ended | |||
|---|---|---|---|---|---|---|
| 
 May 20, 2019  
$ / shares 
 | 
 Sep. 30, 2016  
USD ($)  
$ / shares  
shares 
 | 
 Sep. 30, 2016  
AUD ($)  
$ / shares  
shares 
 | 
 Mar. 31, 2019  
USD ($) 
 | 
Mar. 31, 2018  | 
 Mar. 31, 2017  
USD ($) 
 | 
|
| Dividends Payable [Line Items] | ||||||
| Aggregate cost of common stock repurchased | $ | $ 99.8 | |||||
| Ordinary dividend record date | Jun. 06, 2019 | |||||
| Ordinary dividend payment Date | Aug. 02, 2019 | |||||
| Subsequent Event [Member] | ||||||
| Dividends Payable [Line Items] | ||||||
| Ordinary dividend declared (in dollars per share) | $ / shares | $ 0.26 | |||||
| Fiscal 2017 Program [Member] | ||||||
| Dividends Payable [Line Items] | ||||||
| Aggregate cost of common stock repurchased | $ 99.8 | $ 131.4 | $ 100.0 | |||
| Aggregate number of common stock repurchased and cancelled (in shares) | shares | 6,090,133 | 6,090,133 | ||||
| Average price paid per share of common stock repurchased and cancelled | (per share) | $ 16.40 | $ 21.58 | ||||
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- Definition Aggregate number of shares acquired under a stock repurchase plan. No definition available. 
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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Date the declared dividend will be paid, in CCYY-MM-DD format. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format. No definition available. 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Total cost of shares repurchased divided by the total number of shares repurchased. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Details 
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- Details 
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