Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Schedule of Derivative Instruments) (Details)

v3.7.0.1
Fair Value Measurements (Schedule of Derivative Instruments) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Feb. 01, 2016
Liabilities:        
Asset retirement obligation capitalized $ 6,779 $ 1,914    
Level 1        
Assets:        
Derivative Instruments 0   $ 0  
Liabilities:        
Derivative Instruments 0   0  
Level 2        
Assets:        
Derivative Instruments 42,440   9,184  
Liabilities:        
Derivative Instruments 72,438   145,978  
Level 3        
Assets:        
Derivative Instruments 0   0  
Liabilities:        
Derivative Instruments 0   $ 0  
Asset retirement obligation capitalized $ 6,800      
Level 3 | Investment in Grizzly Oil Sands ULC        
Liabilities:        
Equity investment   $ 39,100    
Level 3 | Investment in Strike Force Midstream LLC        
Liabilities:        
Equity investment       $ 22,500