Annual and transition report of foreign private issuers pursuant to Section 13 or 15(d)

Stock-Based Compensation - Additional Information (Detail)

v3.8.0.1
Stock-Based Compensation - Additional Information (Detail)
$ in Millions
12 Months Ended
Sep. 18, 2017
shares
Aug. 21, 2017
shares
Sep. 16, 2016
shares
Sep. 16, 2015
shares
Sep. 16, 2014
shares
Sep. 16, 2013
shares
Mar. 31, 2018
USD ($)
shares
Mar. 31, 2018
AUD ($)
shares
Mar. 31, 2017
USD ($)
shares
Mar. 31, 2017
AUD ($)
shares
Mar. 31, 2016
USD ($)
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Unrecognized compensation cost related to stock-based compensation cost | $             $ 19,000,000        
Estimated weighted average amortization, period of recognition             2 years 2 months 24 days 2 years 2 months 24 days      
Restricted stock units outstanding (in shares)             4,137,592   3,340,245 3,340,245 4,049,454
Intrinsic value of stock options exercised | $               $ 0.8   $ 0.8  
Excess tax benefits from share-based awards | $             $ 0   $ 3,000,000   $ 400,000
Restricted stock units granted (in shares)             1,779,904 1,779,904 1,179,994 1,179,994  
Restricted stock units vested (in shares)             615,334 615,334 1,314,825 1,314,825  
Unvested restricted stock units cancelled (in shares)             367,223 367,223 574,378 574,378  
Scorecard LTI - cash settled units granted under the terms of LTIP (in shares)   1,545,750   458,484              
Average closing price period             20 days 20 days      
Restricted Stock Units Service Vesting [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Restricted stock units granted (in shares)             332,262 332,262 315,636 315,636  
Restricted stock units vested (in shares)             237,480 237,480 304,470 304,470  
Restricted Stock Units Performance Vesting [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
LTI units granted (in shares)   515,249 407,539                
Restricted stock units vested (in shares)             221,042 221,042      
Unvested restricted stock units cancelled (in shares) 165,040                    
Restricted Stock Units (Market Condition) [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Restricted stock units granted (in shares)   932,393 456,819                
Restricted stock units vested (in shares)             156,812 156,812 728,887 728,887  
Long Term Incentive Award [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
LTI units granted (in shares) 197,800   316,841   454,179 518,647          
2001 Plan [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Issue of shares authorized (in shares)             45,077,100        
Percentage of grants exercised after first year (as percent)             25.00% 25.00%      
Percentage of grants exercised after second year (as percent)             25.00% 25.00%      
Percentage of grants exercised after third year (as percent)             50.00% 50.00%      
Unexercised grants expiration year             10 years 10 years      
Unexercised grants expiration days             90 days 90 days      
Restricted stock units outstanding (in shares)             620,544        
Long-Term Incentive Plan 2006 [Member]                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Restricted stock units outstanding (in shares)             3,517,048        
LTI units granted (in shares)             12,475,138 12,475,138