Summary of Significant Accounting Policies (Details)		1 Months Ended	2 Months Ended	3 Months Ended								11 Months Ended	12 Months Ended
	Apr. 01, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 $ / bbl	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) $ / bbl	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Mar. 25, 2019 USD ($)	Feb. 22, 2019 $ / shares	Jan. 01, 2019 USD ($)	Dec. 30, 2018 USD ($)	Feb. 09, 2018 USD ($)	Feb. 08, 2018 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Vesting period												3 years
2024 Notes																			$ 533,600,000
Other write-downs and impairment expense													$ 0	$ 0
Liability for uncertain tax positions				$ 0				$ 0				$ 0	0	0
Income tax penalties and interest													0	0
Investment in LLC — cost								9,000,000						$ 9,000,000
Net loss			$ 34,571,000	2,037,170,000	$ (17,844,000)	$ 22,477,000		$ 35,733,000	$ 22,163,000	$ (15,620,000)	$ (29,430,000)	2,076,374,000	2,000,000,000
Current liabilities in excess of current assets				68,500,000								$ 68,500,000	$ 68,500,000
Base Price Per Unit for Crude Oil | $ / bbl							40					65.56
Minimum | Other Property And Equipment
Summary Of Significant Accounting Policies [Line Items]
Depreciable life of property and equipment													3 years
Maximum | Other Property And Equipment
Summary Of Significant Accounting Policies [Line Items]
Depreciable life of property and equipment													7 years
7.875% Senior Unsecured Notes Due 2024
Summary Of Significant Accounting Policies [Line Items]
2024 Notes				500,000,000								$ 500,000,000	$ 500,000,000
Alta Mesa Holdings LP | 7.875% Senior Unsecured Notes Due 2024
Summary Of Significant Accounting Policies [Line Items]
2024 Notes				500,000,000								500,000,000	500,000,000
Alta Mesa Holdings LP | 7.875% Senior Unsecured Notes Due 2024
Summary Of Significant Accounting Policies [Line Items]
2024 Notes				500,000,000								500,000,000	500,000,000
Fair value of senior notes payable				533,600,000								533,600,000	533,600,000
ASU 2016-02 | Forecast
Summary Of Significant Accounting Policies [Line Items]
Lease liability																	$ 20,000,000
Right-of-use asset																	$ 20,000,000
Subsequent Event
Summary Of Significant Accounting Policies [Line Items]
Unsecured Debt															$ 500,000,000
Subsequent Event | Forecast
Summary Of Significant Accounting Policies [Line Items]
Periodic interest payment		$ 20,000,000
AMR | Common Class A | Subsequent Event
Summary Of Significant Accounting Policies [Line Items]
Common stock par value (in dollars per share) | $ / shares																$ 1.00
Alta Mesa Credit Facility
Summary Of Significant Accounting Policies [Line Items]
Credit facility amount				$ 400,000,000								$ 400,000,000	$ 400,000,000					$ 370,000,000		$ 1,000,000,000
Alta Mesa Credit Facility | Subsequent Event
Summary Of Significant Accounting Policies [Line Items]
Credit facility amount	$ 370,000,000
Credit facility amount drew	$ 70,000,000