SIGNIFICANT ACQUISITIONS AND DIVESTITURES (Narrative) (Details) - USD ($)		1 Months Ended		3 Months Ended	11 Months Ended	12 Months Ended		24 Months Ended
	Feb. 09, 2018	Oct. 31, 2018	Feb. 08, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019
Business Acquisition [Line Items]
Proceeds from stock issued			$ 0		$ 400,000,000	$ 0
Common stock par value (in dollars per share)					$ 0.0001	$ 0.0001	$ 0.0001	$ 0.0001
SRII Opco, LP
Business Acquisition [Line Items]
Economic interests						47.75%		47.75%
SRII Opco, LP | Common Units
Business Acquisition [Line Items]
Shares issued to acquire business (in shares)	59,871,031
Common Class A
Business Acquisition [Line Items]
Shares sold (in shares)							3,101,510
Common Class C
Business Acquisition [Line Items]
Shares issued during period (in shares)						213,402,398
Common stock par value (in dollars per share)	$ 0.0001
SRII Opco, LP
Business Acquisition [Line Items]
Ownership interest						44.20%		44.20%
KFM Credit Facility
Business Acquisition [Line Items]
Payment towards acquisition of all working interests	$ 809,812,000
KFM Credit Facility | SRII Opco, LP
Business Acquisition [Line Items]
Shares issued to acquire business (in shares)	55,000,000
Common stock par value (in dollars per share)	$ 7.90
Alta Mesa | SRII Opco, LP
Business Acquisition [Line Items]
Common stock par value (in dollars per share)	$ 7.90
SRII Opco, LP
Business Acquisition [Line Items]
Percentage of ownership acquired	44.20%
Payment towards acquisition of all working interests	$ 1,338,000,000
Number of shares acquired (in shares)	169,371,730
Number of warrants acquired (in shares)	62,966,651
Alta Mesa, Alta Mesa GP, And Kingfisher | SRII Opco, LP
Business Acquisition [Line Items]
Shares issued to acquire business (in shares)	213,402,398
Percentage of outstanding shares issued	55.80%
Alta Mesa Holdings GP, LLC
Business Acquisition [Line Items]
Contribution to affiliates	$ 560,000,000.0
Alta Mesa Holdings GP, LLC | SRII Opco, LP
Business Acquisition [Line Items]
Economic interests	100.00%
Percentage of ownership acquired	90.00%
Fenter Energy, LLC
Business Acquisition [Line Items]
Cash		$ 22,300,000
SRII Opco, LP | Common Class A
Business Acquisition [Line Items]
Conversion of common shares (in shares)						2,181,600	12,341,076	14,522,676
SRII Opco, LP | KFM Credit Facility
Business Acquisition [Line Items]
Economic interests	100.00%
SRII Opco, LP | Alta Mesa
Business Acquisition [Line Items]
Percentage of ownership acquired	90.00%
Riverstone VI SR II Holdings, L.P. | Common Class A
Business Acquisition [Line Items]
Shares issued during period (in shares)	40,000,000
Warrants issued (in shares)	13,333,333
Proceeds from stock issued	$ 400,000,000
KFM Contributor
Business Acquisition [Line Items]
Shares issued to acquire business (in shares)				89,680
KFM Contributor | SRII Opco, LP
Business Acquisition [Line Items]
Contribution to affiliates	$ 814,800,000
Minority Voting Interest Holders In Alta Mesa GP
Business Acquisition [Line Items]
Percentage of ownership acquired	10.00%
AM Contributor
Business Acquisition [Line Items]
Shares issued to acquire business (in shares)				1,197,934
AM Contributor | Alta Mesa | SRII Opco, LP
Business Acquisition [Line Items]
Shares issued to acquire business (in shares)	138,402,398