Quarterly report pursuant to Section 13 or 15(d)

Leased Properties and Leases - Significant Leases (Details)

v3.10.0.1
Leased Properties and Leases - Significant Leases (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Pinedale LGS [Member]          
Operating Leased Assets [Line Items]          
Percentage of total leased properties 39.90%   39.90%   39.90%
Percentage of leased property revenue 35.30% 30.60% 34.10% 30.60%  
Variable rent $ 1.1   $ 1.5    
Grand Isle Gathering System [Member]          
Operating Leased Assets [Line Items]          
Percentage of total leased properties 49.70%   49.70%   49.70%
Percentage of leased property revenue 55.60% 59.60% 56.70% 59.60%  
Portland Terminal Facility [Member]          
Operating Leased Assets [Line Items]          
Percentage of total leased properties 10.20%   10.20%   10.10%
Percentage of leased property revenue 9.00% 9.60% 9.10% 9.70%