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Financial Instrument - Risk Management and Fair Value - Summary of Carrying Amount and Fair Values of Financial Assets and Financial Liabilities (Detail) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Disclosure of detailed information about financial instruments [line items]        
Cash and cash equivalents $ 238,792 $ 331,687 $ 204,715 $ 221,443
Short-term investments 705,108 483,002 480,233  
Account receivable 118,085 116,100    
Long-term investments 65,953 953 $ 861  
Debt 1,174,581 1,184,132    
Account payable 129,434 112,857    
Derivative financial liabilities   2,801    
Financial Assets at Fair Value, Class [Member]        
Disclosure of detailed information about financial instruments [line items]        
Cash and cash equivalents 238,792 331,687    
Short-term investments 705,108 483,002    
Account receivable 118,085 116,100    
Long-term investments 65,953 953    
Fuel derivative instruments [member]        
Disclosure of detailed information about financial instruments [line items]        
Derivative financial liabilities   2,801    
Financial Liabilities at Fair Value, Class [Member]        
Disclosure of detailed information about financial instruments [line items]        
Debt 1,053,070 1,062,952    
Account payable $ 129,434 112,857    
Financial Liabilities at Fair Value, Class [Member] | Fuel derivative instruments [member]        
Disclosure of detailed information about financial instruments [line items]        
Derivative financial liabilities   $ 2,801