Acquisitions and Divestitures (Details) - USD ($) $ in Thousands, shares in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Combination, Separately Recognized Transactions [Line Items]
Business Combination, Separately Recognized Transactions, Additional Disclosures, Acquisition Cost Expensed	$ 5,000
Accounts Receivable, Net	83,540
Inventories	10,955
Other	10,640
Total Current Assets	175,546
Oil and Gas Properties (Successful Efforts Method)	3,850,100
Other Property, Plant and Equipment	16,586
Total Property, Plant and Equipment, Net	3,866,686
Other Assets	22,706
Total Assets	4,064,938
Accounts Payable	126,988
Accrued Taxes Payable	23,520
Other	743
Total Current Liabilities	151,251
Long-Term Debt	163,829
Asset Retirement Obligations	163,144
Off-Market Transportation Contracts	39,720
Other Liabilities	28,645
Deferred Income Taxes	1,104,581
Total Liabilities	1,651,170
Total Consideration Transferred	2,413,768
Gains (Losses) on Asset Dispositions, Net	205,835	$ (8,798)	$ 507,590
Proceeds from Sale of Producing Properties	$ 1,119,215	192,807	569,332
Stock Issued During Period, Shares, Acquisitions	25
Payments to Acquire Businesses, Gross	$ 16,000
Aggregated Purchase Price to Acquire Proved Crude Oil Properties and Related Assets		$ 481,000
Cumulative translation adjustments	383,000
Restricted cash related to future abandonment liabilities			$ 150,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	2,400,000
Cash Acquired from Acquisition	70,411
Revenue [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Business Combination, Separately Recognized Transactions, Revenues and Gains Recognized	71,000
Operating Income [Member]
Business Combination, Separately Recognized Transactions [Line Items]
Business Combination, Separately Recognized Transactions, Expenses and Losses Recognized	$ 8,000