Debt - Credit Facility (Details)		3 Months Ended		9 Months Ended
	Mar. 25, 2016 USD ($) vessel drillship	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) drilling_unit	Jun. 30, 2015 USD ($)
Line of Credit Facility [Line Items]
Number of drilling units | drilling_unit				9
Revolving Credit Facility
Line of Credit Facility [Line Items]
Minimum interest expense coverage ratio	1.15
Minimum liquidity financial covenant	$ 150,000,000
Long-term line of credit, reduction in borrowing capacity	$ 152,000,000
Long-term line of credit, maximum borrowing capacity		$ 1,395,000,000		$ 1,395,000,000
Number of vessels pledged as collateral | vessel	3
Number of vessels removed as collateral | vessel	2
Number of drillships unencumbered | drillship	2
Long-term line of credit		885,000,000		885,000,000
Long-term line of credit, remaining borrowing capacity		$ 510,000,000		$ 510,000,000
Weighted average interest rate		4.36%		4.36%
Interest costs capitalized		$ 4,200,000	$ 6,000,000	$ 12,800,000	$ 15,000,000
Revolving Credit Facility | Minimum | Eurodollar
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.50%
Unused capacity commitment fee	1.00%
Revolving Credit Facility | Maximum | Eurodollar
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.25%
Unused capacity commitment fee	1.30%
Revolving Credit Facility, Maturing May 2018 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Long-term line of credit, maximum borrowing capacity	$ 1,395,000,000.000	275,000,000		275,000,000
Revolving Credit Facility, Maturing May 2019 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Long-term line of credit, maximum borrowing capacity	1,120,500,000.0000	$ 1,120,000,000		$ 1,120,000,000
Junior Lien | Revolving Credit Facility
Line of Credit Facility [Line Items]
Long-term line of credit, maximum borrowing capacity	$ 400,000,000