Derivative Financial Instruments - Additional Information (Details)	9 Months Ended
Sep. 30, 2018
Maximum
Derivative [Line Items]
Commodity derivatives board authorization	50.00%

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