Segment Information - Income Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Sep. 30, 2015
Segment information
Total assets	$ 7,025,105		$ 7,025,105		$ 7,147,242
Operating revenues	438,191	$ 885,670	926,038	$ 1,946,457
United States
Segment information
Operating revenues	385,977	778,637	795,483	1,734,918
Argentina
Segment information
Operating revenues	35,371	46,273	85,157	74,749
Colombia
Segment information
Operating revenues	4,602	22,691	11,345	46,628
Ecuador
Segment information
Operating revenues	527	5,510	4,467	19,400
Other foreign
Segment information
Operating revenues	11,714	32,559	29,586	70,762
Continued operations
Segment information
Total assets	7,024,875		7,024,875		7,139,145
Discontinued operations.
Segment information
Total assets	230		230		8,097
Other
Segment information
Operating revenues	3,231	3,741	7,199	7,921
Operating segment
Segment information
Total assets	5,888,338		5,888,338		6,152,140
Operating revenues	438,401	885,890	926,467	1,946,899
Operating segment | U.S. Land
Segment information
Total assets	5,210,465		5,210,465		5,429,179
Operating segment | Offshore
Segment information
Total assets	110,446		110,446		118,852
Operating segment | International Land
Segment information
Total assets	530,310		530,310		565,712
Operating segment | Other
Segment information
Total assets	37,117		37,117		38,397
Operating revenues	3,441	$ 3,961	7,628	$ 8,363
Investments and corporate operations
Segment information
Total assets	$ 1,136,537		$ 1,136,537		$ 987,005