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Discontinued Operation - Additional Information (Detail)
$ in Millions, $ in Millions
 12 Months Ended
Oct. 02, 2017
USD ($)
Oct. 02, 2017
AUD ($)
Dec. 31, 2018
USD ($)
shares
Dec. 31, 2018
AUD ($)
shares
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Oct. 31, 2018
AUD ($)
Disclosure Of Noncurrent Assets Held For Sale And Discontinued Operations [line items]              
Profit on the sale assets     $ 0.0   $ 0.0 $ (2.3)  
Darlot [Member]              
Disclosure Of Noncurrent Assets Held For Sale And Discontinued Operations [line items]              
Consideration from disposal       $ 18.5      
Cash consideration from disposal       $ 12.0      
Number of shares received from disposal | shares     130,000,000 130,000,000      
Upfront cash consideration received     $ 0.0 $ 7.0 $ 5.4 $ 0.0  
Cash consideration receivable       $ 5.0     $ 5.0
Profit on the sale assets $ 23.5 $ 30.8          
Percentage of shares held 19.90% 19.90%          
Darlot [Member] | Red 5 Limited [Member]              
Disclosure Of Noncurrent Assets Held For Sale And Discontinued Operations [line items]              
Shares received under underwriting agreement related to disposal of discontinued operation | shares       116,875,821      
Consideration received under underwriting agreement related to disposal of discontinued operation       $ 5.8