XML 58 R43.htm IDEA: XBRL DOCUMENT v3.8.0.1
Summary of Significant Accounting Policies - Narrative (Details)
12 Months Ended
Dec. 31, 2017
USD ($)
Customer
Institution
Segment
Dec. 31, 2016
USD ($)
Customer
Dec. 31, 2015
USD ($)
Customer
Jan. 01, 2017
USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]        
Number of operating segments | Segment 1      
Number of financial institutions | Institution 4      
Amortization of unproved properties included in depreciation, depletion, and amortization $ 52,800,000 $ 25,000,000 $ 41,400,000  
Assets legally restricted for purposes of settling asset retirement obligations 0      
Properties and Equipment        
Net Cash Provided by Operating Activities 898,160,000 397,441,000 749,598,000  
Net cash provided by financing activities $ 210,502,000 $ (453,805,000) $ (223,296,000)  
Gathering and pipeline systems and equipment | Minimum        
Properties and Equipment        
Estimated useful life 10 years      
Gathering and pipeline systems and equipment | Maximum        
Properties and Equipment        
Estimated useful life 25 years      
Buildings | Minimum        
Properties and Equipment        
Estimated useful life 25 years      
Buildings | Maximum        
Properties and Equipment        
Estimated useful life 40 years      
Other assets | Minimum        
Properties and Equipment        
Estimated useful life 3 years      
Other assets | Maximum        
Properties and Equipment        
Estimated useful life 10 years      
Sales Revenue, Net | Customer        
Concentration Risk [Line Items]        
Number of customers | Customer 2 2 2  
Customer one | Sales Revenue, Net | Customer        
Concentration Risk [Line Items]        
Percentage of total sales 18.00% 19.00% 16.00%  
Customer two | Sales Revenue, Net | Customer        
Concentration Risk [Line Items]        
Percentage of total sales 11.00% 10.00% 14.00%  
Accounting Standards Update 2016-09, Excess Tax Benefit Component        
Properties and Equipment        
Cumulative effect adjustment       $ 42,200,000
Accounting Standards Update 2017-07        
Properties and Equipment        
Other expense (income)   $ 1,600,000 $ 1,400,000