Segment Information - Income Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016
Segment information
Total assets	$ 6,513,891		$ 6,513,891		$ 6,832,019
Operating revenues	498,564	$ 366,486	1,272,437	$ 1,292,524
United States
Segment information
Operating revenues	443,489	318,059	1,114,574	1,113,542
Argentina
Segment information
Operating revenues	43,167	33,208	114,516	118,365
Colombia
Segment information
Operating revenues	9,356	3,831	27,579	15,176
Ecuador
Segment information
Operating revenues	3	481	5	4,948
Other Foreign
Segment information
Operating revenues	2,549	10,907	15,763	40,493
Continued operations
Segment information
Total assets	6,513,884		6,513,884		6,831,955
Discontinued operations.
Segment information
Total assets	7		7		64
Other
Segment information
Operating revenues	4,262	2,983	10,697	10,182
Operating segment
Segment information
Total assets	5,624,977		5,624,977		5,633,773
Operating revenues	498,786	366,692	1,273,075	1,293,159
Operating segment | U.S. Land
Segment information
Total assets	4,974,364		4,974,364		5,005,299
Operating segment | Offshore
Segment information
Total assets	98,568		98,568		105,152
Operating segment | International Land
Segment information
Total assets	417,241		417,241		487,181
Operating segment | Other
Segment information
Total assets	134,804		134,804		36,141
Operating revenues	4,484	$ 3,189	11,335	$ 10,817
Investments and corporate operations
Segment information
Total assets	$ 888,907		$ 888,907		$ 1,198,182