Segment Information - Income Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Segment information
Total assets	$ 6,677,637		$ 6,832,019
Operating revenues	368,590	$ 487,847
United States
Segment information
Operating revenues	300,559	409,506
Argentina
Segment information
Operating revenues	48,082	49,786
Colombia
Segment information
Operating revenues	9,371	6,743
Ecuador
Segment information
Operating revenues	1	3,940
Other foreign
Segment information
Operating revenues	10,577	17,872
Continued operations
Segment information
Total assets	6,677,586		6,831,955
Discontinued operation
Segment information
Total assets	51		64
Other
Segment information
Operating revenues	3,111	3,968
Operating segment
Segment information
Total assets	5,534,115		5,633,773
Operating revenues	368,798	488,066
Operating segment | U.S. Land
Segment information
Total assets	4,933,281		5,005,299
Operating segment | Offshore
Segment information
Total assets	106,860		105,152
Operating segment | International Land
Segment information
Total assets	457,566		487,181
Operating segment | Other
Segment information
Total assets	36,408		36,141
Operating revenues	3,319	$ 4,187
Investments and corporate operations
Segment information
Total assets	$ 1,143,471		$ 1,198,182