Revenue from Contracts with Customers (Narrative) (Details)	12 Months Ended	36 Months Ended
Dec. 31, 2018 USD ($) contract segment agreement item	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Disaggregation of Revenue [Line Items]
Number of geographic segments \| segment	3
Number of revenue streams \| item	3
Number of production sharing contracts \| contract	7
Receivables from contracts with customers	$ 263,000,000	$ 263,000,000	$ 203,400,000
Impairment losses on receivables or contract assets		$ 0
Malaysia [Member]
Disaggregation of Revenue [Line Items]
Number of gas sale agreements \| agreement	3

Amount of credit loss recognized for write-down of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130551-203045

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=82913815&loc=SL49130533-203044

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045

Name:	us-gaap_ContractWithCustomerAssetCreditLossExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration