Property and Equipment - Summary of Property and Equipment by Classification (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014
Property, Plant and Equipment
Total cost	$ 4,535,823	$ 4,568,153
Less: Accumulated depreciation	(522,650)	(601,125)
Property and equipment, net	4,013,173	3,967,028
Drilling vessels and equipment
Property, Plant and Equipment
Total cost	4,021,901	4,181,774
Construction work in progress
Property, Plant and Equipment
Total cost	437,939	319,548
Drill pipe
Property, Plant and Equipment
Total cost	40,141	31,265
Office equipment and other
Property, Plant and Equipment
Total cost	$ 35,842	$ 35,566