Property and Equipment - Summary of Property and Equipment by Classification (Details) - USD ($) $ in Thousands	Jun. 30, 2015	Sep. 30, 2014
Property, Plant and Equipment
Total cost	$ 4,795,760	$ 4,568,153
Less: Accumulated depreciation	(606,966)	(601,125)
Property and equipment, net	4,188,794	3,967,028
Drilling vessels and equipment
Property, Plant and Equipment
Total cost	4,032,126	4,181,774
Construction work in progress
Property, Plant and Equipment
Total cost	684,522	319,548
Drill pipe
Property, Plant and Equipment
Total cost	42,734	31,265
Office equipment and other
Property, Plant and Equipment
Total cost	$ 36,378	$ 35,566