Supplemental Cash Flow Information - Operating assets and liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Components of operating assets and liabilities
Decrease (increase) in restricted cash	$ 33	$ 28
Decrease (increase) in accounts receivable	122,829	(55,150)
Decrease (increase) in receivable from affiliates	754	12,529
Decrease (increase) in inventories	25,220	(2,441)
Decrease (increase) in other current assets	(3,748)	857
Decrease (increase) in other assets	805	(875)
Increase (decrease) in accounts payable and accrued liabilities	(104,888)	40,485
Increase (decrease) in payable to affiliates	(4,650)	(9,422)
Increase (decrease) in other noncurrent liabilities	16,142	1,041
Total changes in operating assets and liabilities	$ 52,497	$ (12,948)