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Equity - Exchangeable Shares and Series F and Series G Preferred Stock (Detail)
 12 Months Ended
Oct. 06, 2017
shares
Dec. 31, 2017
Acquisition
shares
Dec. 31, 2016
shares
Dec. 31, 2015
shares
Oct. 05, 2017
shares
Class of Stock [Line Items]          
Number of shares of Common stock received for each exchangeable share (in shares)   1      
Minimum number of shares that can be exchanged by exchangeable shareholders unless the number of remaining exchangeable shares registered in the name of the holder is less (in shares)   50,000      
Number of business acquisitions having issuances of preferred stock | Acquisition   2      
Common stock, shares outstanding (in shares)   153,342,326 144,710,773    
Series F Preferred Stock          
Class of Stock [Line Items]          
Preferred stock, shares issued (in shares)   0 1   1
Preferred stock, shares retired (in shares) 1 1      
Preferred stock, shares outstanding (in shares)   0 1    
Series G Preferred Stock          
Class of Stock [Line Items]          
Preferred stock, shares issued (in shares)   1 1    
Preferred stock, shares outstanding (in shares)   1 1    
Exchangeable Shares For Common Stock          
Class of Stock [Line Items]          
Exchangeable shares exchanged for common stock (in shares)   6,000,000 400,000 400,000  
Exchangeable Shares          
Class of Stock [Line Items]          
Common stock, shares outstanding (in shares)   486,112 6,515,453    
Exchangeable Shares Associated with Series G Preferred Stock          
Class of Stock [Line Items]          
Common stock, shares outstanding (in shares)   400,000