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Supplemental Cash Flow Information (Tables)
 12 Months Ended
Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]  
Changes in Operating Assets and Liabilities
a)The changes in operating assets and liabilities for the years ended December 31, 2017, 2016, and 2015, are as follows:
 
Year Ended December 31,
 
2017
 
2016
 
2015
Accounts receivable
(1,925
)
 
96,497

 
(6,488
)
Prepaid expenses and other
2,608

 
9,690

 
(10,607
)
Accounts payable
(14,499
)
 
(10,705
)
 
(24,727
)
Accrued liabilities and other
120,383

 
(57,149
)
 
29,531

 
106,567

 
38,333

 
(12,291
)