Supplemental Cash Flow Information - Operating assets and liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018
Components of operating assets and liabilities
Decrease (increase) in restricted cash	$ 0	$ 33
Decrease (increase) in accounts receivable	(100,365)	99,923
Decrease (increase) in receivable from affiliates	(887)	(92)
Decrease (increase) in inventories	(12,515)	40,051
Decrease (increase) in other current assets	(6,982)	(7,338)
Decrease (increase) in other assets	1,027	(3,702)
Increase (decrease) in accounts payable and accrued liabilities	35,487	(111,712)
Increase (decrease) in payable to affiliates	(473)	(6,088)
Increase (decrease) in other noncurrent liabilities	8,765	424
Total changes in operating assets and liabilities	$ (75,943)	$ 11,499

The increase (decrease) during the reporting period in receivables to be collected from an entity that is controlling, under the control of, or within the same control group as the reporting entity by means of direct or indirect ownership.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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The increase (decrease) during the reporting period in the amounts payable to vendors for goods and services received and the amount of obligations and expenses incurred but not paid.

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The increase (decrease) during the reporting period in amount due within one year (or one business cycle) from customers for the credit sale of goods and services.

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The increase (decrease) in obligations owed to an entity that is controlling, under the control of, or within the same control group as the reporting entity by means of direct or indirect ownership.

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The increase (decrease) during the reporting period in the aggregate value of all inventory held by the reporting entity, associated with underlying transactions that are classified as operating activities.

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The increase (decrease) during the reporting period of all assets and liabilities used in operating activities.

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Amount of increase (decrease) in current assets classified as other.

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
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-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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Amount of increase (decrease) in noncurrent assets classified as other.

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Amount of increase (decrease) in noncurrent operating liabilities classified as other.

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The net cash inflow or outflow for the increase (decrease) associated with funds that are not available for withdrawal or use (such as funds held in escrow) and are associated with underlying transactions that are classified as investing activities.

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