Segment Information - Income Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Sep. 30, 2015
Segment information
Total assets	$ 6,976,519		$ 6,976,519		$ 7,147,242
Operating revenues	366,486	$ 661,445	1,292,524	$ 2,607,902
United States
Segment information
Operating revenues	318,059	547,043	1,113,542	2,281,961
Argentina
Segment information
Operating revenues	33,208	53,778	118,365	128,527
Colombia
Segment information
Operating revenues	3,831	13,772	15,176	60,400
Ecuador
Segment information
Operating revenues	481	6,864	4,948	26,264
Other foreign
Segment information
Operating revenues	10,907	39,988	40,493	110,750
Continued operations
Segment information
Total assets	6,976,439		6,976,439		7,139,145
Discontinued operations.
Segment information
Total assets	80		80		8,097
Other
Segment information
Operating revenues	2,983	3,208	10,182	11,129
Operating segment
Segment information
Total assets	5,751,034		5,751,034		6,152,140
Operating revenues	366,692	661,649	1,293,159	2,608,562
Operating segment | U.S. Land
Segment information
Total assets	5,113,421		5,113,421		5,429,179
Operating segment | Offshore
Segment information
Total assets	108,656		108,656		118,852
Operating segment | International Land
Segment information
Total assets	493,207		493,207		565,712
Operating segment | Other
Segment information
Total assets	35,750		35,750		38,397
Operating revenues	3,189	$ 3,412	10,817	$ 11,789
Investments and corporate operations
Segment information
Total assets	$ 1,225,405		$ 1,225,405		$ 987,005