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Convertible Notes, Net - Summary of Outstanding Convertible Senior Notes (Parenthetical) (Detail)
1 Months Ended 9 Months Ended
Jun. 28, 2017
USD ($)
$ / shares
May 31, 2017
USD ($)
$ / shares
Nov. 30, 2013
USD ($)
$ / shares
Sep. 30, 2017
4.38% Convertible Senior Notes [Member]        
Debt Instrument [Line Items]        
Convertible Notes, debt conversion, common stock issued, in percent       28.0324
4.38% Convertible Senior Notes [Member] | Class A Common Stock [Member]        
Debt Instrument [Line Items]        
Convertible Notes, debt conversion, principal amount | $   $ 1,000    
Debt instrument, conversion price | $ / shares   $ 35.67    
Convertible Notes, debt conversion, common stock issued, in percent   27.6700    
Convertible Senior Notes [Member] | Class A Common Stock [Member]        
Debt Instrument [Line Items]        
Convertible Notes, debt conversion, principal amount | $ $ 1,000   $ 1,000  
Debt instrument, conversion price | $ / shares $ 27.99   $ 35.67  
Convertible Notes, debt conversion, common stock issued, in percent 35.7236   27.6700