Segment Information - Total assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Segment information
Assets	$ 6,261,792	$ 6,439,988
Operating segment
Segment information
Assets	5,623,400	5,613,084
Investments and corporate operations
Segment information
Assets	638,392	826,901
U.S. Land | Operating segment
Segment information
Assets	4,940,149	4,967,074
Offshore | Operating segment
Segment information
Assets	101,350	99,533
International Land | Operating segment
Segment information
Assets	399,898	413,392
Other | Operating segment
Segment information
Assets	182,003	133,085
Continued operations
Segment information
Assets	$ 6,261,792	6,439,985
Discontinued operations.
Segment information
Assets		$ 3