PROPERTY AND EQUIPMENT - Summary of Property and Equipment by Classification (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment
Total cost	$ 4,876,049	$ 4,848,014
Less: Accumulated depreciation	(738,308)	(720,318)
Property and equipment, net	4,137,741	4,127,696
Drilling vessels and equipment
Property, Plant and Equipment
Total cost	3,775,450	3,898,686
Construction work in progress
Property, Plant and Equipment
Total cost	1,010,092	857,572
Drill pipe
Property, Plant and Equipment
Total cost	51,334	52,543
Office equipment and other
Property, Plant and Equipment
Total cost	$ 39,173	$ 39,213