Supplemental Cash Flow Information - Changes in Operating Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Decrease (increase):
Accounts receivable	$ (3,077)	$ 2,154
Accounts receivable from related parties	(2,933)	(1,128)
Inventories	(987)	(114)
Other current assets	848	1,416
Other assets	(519)	(825)
Increase (decrease):
Accounts payable	2,838	(63)
Accounts payable to related parties	1,416	488
Motor fuel taxes payable	117	(426)
Accrued expenses and other current liabilities	(590)	(688)
Other long-term liabilities	678	(382)
Changes in operating assets and liabilities, net of acquisitions	$ (2,209)	$ 432

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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The increase (decrease) during the reporting period in the obligations due for goods and services provided by the following types of related parties: a parent company and its subsidiaries, subsidiaries of a common parent, an entity and trust for the benefit of employees, such as pension and profit-sharing trusts that are managed by or under the trusteeship of the entities' management, an entity and its principal owners, management, or member of their immediate families, affiliates, or other parties with the ability to exert significant influence.

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- Definition

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 amount due to the reporting entity for good and services provided to the following types of related parties: a parent company and its subsidiaries; subsidiaries of a common parent; an entity and trust for the benefit of employees, such as pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management, an entity and its principal owners, management, member of their immediate families, affiliates, or other parties with the ability to exert significant influence.

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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 of all taxes owed but not paid, including income, property and other taxes.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

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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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Amount of increase (decrease) in current operating assets after deduction of current operating liabilities classified as other.

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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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Amount of increase (decrease) in prepaid expenses, and assets classified as other.

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