Supplemental Cash Flow Information (Net Changes in Components of Operating Assets and Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
(Increase) decrease in:
Accounts receivable	$ 27,368	$ 9,169
Inventories	(4,469)	6,009
Deferred charges	(4,161)	(348)
Other current assets	(7,694)	(4,605)
Increase (decrease) in:
Accounts payable	94	(17,305)
Accrued liabilities	(14,920)	(21,988)
Net changes in components of operating assets and liabilities	$ (3,782)	$ (29,068)

The increase (decrease) during the reporting period in the aggregate amount of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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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) during the reporting period in the aggregate amount of expenses incurred but not yet paid.

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The increase (decrease) during the reporting period in the value of expenditures made during the current reporting period for benefits that will be received over a period of years. Deferred charges differ from prepaid expenses in that they usually extend over a long period of time and may or may not be regularly recurring costs of operation.

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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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