Unaudited Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands, shares in Millions	Sep. 30, 2018	Dec. 31, 2017
Accounts receivable, non-trade	$ 9,133	$ 32,387
Accumulated depreciation	$ 1,637,286	$ 1,562,172
Common Units
Limited partners - units issued (shares)	410.3	410.0
Limited partners - units outstanding (shares)	410.3	410.0
Preferred Units
Limited partners - units issued (shares)	15.8	11.0
Limited partners - units outstanding (shares)	15.8	11.0

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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The number of limited partner units issued.

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The number of limited partner units outstanding.

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The sum of amounts currently receivable other than from customers. For classified balance sheets, represents the current amount receivable, that is amounts expected to be collected within one year or the normal operating cycle, if longer.

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