Financial Instruments - Notional amounts (Details) - Not Designated as Hedging Instrument [Member] - Commodity Contract [Member] - bbl bbl in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Short [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	3,406	2,704	12,514	10,467
Long [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	3,243	2,701	12,268	9,892

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration