Significant Acquisitions and Divestitures (Allocation Of Purchase Consideration) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Feb. 09, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
2024 Notes		$ 533,600
Credit facility amount outstanding		134,100
7.875% Senior Unsecured Notes Due 2024
Business Acquisition [Line Items]
2024 Notes	$ 500,000
Stated interest rate of senior notes	7.875%		7.875%
Alta Mesa RBL
Business Acquisition [Line Items]
Cash, cash equivalents and restricted cash		10,345
Accounts receivable		101,745
Other receivables		2,062
Receivables due from related party		907
Prepaid expenses and other		1,405
Derivatives		352
oil and gas properties, successful efforts		2,309,979
Other property and equipment, net		43,318
Notes receivable due from related party		12,454
Deposits and other long-term assets		10,286
Total fair value of assets acquired		2,492,853
Accounts payable and accrued liabilities		197,361
Accounts payable — affiliate		5,476
Advances from non-operators		6,803
Advances from related party		47,506
Asset retirement obligations		5,998
Derivatives		11,585
Long-term debt		667,700
Other long-term liabilities		5,066
Total fair value of liabilities assumed		947,495
Total consideration and fair value		1,545,358
Alta Mesa RBL | 7.875% Senior Unsecured Notes Due 2024
Business Acquisition [Line Items]
2024 Notes	$ 500,000
Fair value of senior notes payable	$ 533,600
Alta Mesa RBL | 7.875% Senior Unsecured Notes Due 2024 | Level 1
Business Acquisition [Line Items]
Fair value of senior notes payable		533,600
As initially reported | Alta Mesa RBL
Business Acquisition [Line Items]
Cash, cash equivalents and restricted cash		10,345
Accounts receivable		101,745
Other receivables		1,222
Receivables due from related party		907
Prepaid expenses and other		1,405
Derivatives		352
oil and gas properties, successful efforts		2,314,858
Other property and equipment, net		43,318
Notes receivable due from related party		12,454
Deposits and other long-term assets		10,286
Total fair value of assets acquired		2,496,892
Accounts payable and accrued liabilities		210,867
Accounts payable — affiliate		5,476
Advances from non-operators		6,803
Advances from related party		47,506
Asset retirement obligations		5,998
Derivatives		11,585
Long-term debt		667,700
Other long-term liabilities		5,066
Total fair value of liabilities assumed		961,001
Total consideration and fair value		1,535,891
Adjustment | Alta Mesa RBL
Business Acquisition [Line Items]
Cash, cash equivalents and restricted cash		0
Accounts receivable		0
Other receivables		840
Receivables due from related party		0
Prepaid expenses and other		0
Derivatives		0
oil and gas properties, successful efforts		(4,879)
Other property and equipment, net		0
Notes receivable due from related party		0
Deposits and other long-term assets		0
Total fair value of assets acquired		(4,039)
Accounts payable and accrued liabilities		(13,506)
Accounts payable — affiliate		0
Advances from non-operators		0
Advances from related party		0
Asset retirement obligations		0
Derivatives		0
Long-term debt		0
Other long-term liabilities		0
Total fair value of liabilities assumed		(13,506)
Total consideration and fair value		$ 9,467