INVESTMENT IN OIL AND GAS PROPERTIES - Ownership Interests (Details) - Guinea Concession - m	Sep. 08, 2017	Jul. 12, 2017	Jun. 30, 2017	Jun. 02, 2017
INVESTMENT IN OIL AND GAS PROPERTIES
Ownership interest in Guinea Concession (as a percent)			37.00%
SAPETRO
INVESTMENT IN OIL AND GAS PROPERTIES
Ownership interest sold (as a percent)				50.00%
Tullow Guinea Ltd
INVESTMENT IN OIL AND GAS PROPERTIES
Ownership interest sold (as a percent)			40.00%
Dana
INVESTMENT IN OIL AND GAS PROPERTIES
Ownership interest sold (as a percent)			23.00%
Subsequent Event
INVESTMENT IN OIL AND GAS PROPERTIES
Appraisal period		2 years
Interval (in meters)	5