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Equity (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended 12 Months Ended
May 17, 2018
Feb. 15, 2017
Sep. 30, 2018
Sep. 30, 2018
Sep. 30, 2017
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Options granted in period (in shares)   563,408        
Share price (in dollars per share)   $ 29.68        
Fair value   $ 26,900        
Cost to issue equity $ 100     $ 146 $ 0  
Repayments of Long-term Lines of Credit     $ 45,000      
Restricted Stock            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares granted in period (in shares)   667,488        
Vesting period of shares   3 years        
Corporate Joint Venture | San Mateo Midstream            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Performance incentives earned       14,700    
Deferred performance incentives       $ 58,800   $ 73,500
Deferred performance incentives term       4 years   5 years
Public Stock Offering [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Sale of Stock, Consideration Received on Transaction $ 226,500          
Public Stock Offering [Member] | Common Stock [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Sale of Stock, Number of Shares Issued in Transaction 7,000,000.0