Supplemental Cash Flow Information - Operating assets and liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Components of operating assets and liabilities
Decrease (increase) in restricted cash	$ (3)	$ 1
Decrease (increase) in accounts receivable	43,717	(60,062)
Decrease (increase) in receivable from affiliates	16,805	(4,305)
Decrease (increase) in inventories	19,994	(15,918)
Decrease (increase) in derivatives and margin deposits	1,778	(2,234)
Decrease (increase) in other current assets	(4,812)	956
Decrease (increase) in other assets	(14,710)	(1,266)
Increase (decrease) in accounts payable and accrued liabilities	(28,909)	60,867
Increase (decrease) in payable to affiliates	(23,000)	3,997
Increase (decrease) in other noncurrent liabilities	1,739	(1,453)
Total changes in operating assets and liabilities	$ 12,599	$ (19,417)