Segment Reporting - Risk (Details)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2016
USD ($)
Sep. 30, 2016
USD ($)
Jun. 30, 2016
USD ($)
Mar. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Sep. 30, 2015
USD ($)
Jun. 30, 2015
USD ($)
Mar. 31, 2015
USD ($)
Dec. 31, 2016
USD ($)
customer
Dec. 31, 2015
USD ($)
customer
Dec. 31, 2014
USD ($)
customer
Segment Reporting                      
Number of Major Customers | customer                 0 0 1
Total revenues $ 2,312,430 $ 2,030,198 $ 2,146,199 $ 1,750,812 $ 2,169,445 $ 2,486,203 $ 2,680,088 $ 2,979,116 $ 8,239,639 $ 10,314,852 $ 17,269,954
Wholesale Segment                      
Segment Reporting                      
Total revenues                 $ 4,107,021 $ 5,911,285 12,896,129
Wholesale Segment | Sales Revenue | Customer | ExxonMobil                      
Segment Reporting                      
Total revenues                     $ 2,900,000
Percentage of revenues                     17.00%