DEBT (Credit Facility Narrative) (Details)		12 Months Ended
	Mar. 25, 2016 USD ($) drilling_unit vessel drillship	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)
Line of Credit Facility [Line Items]
Number of drilling units | drilling_unit	8
Standby letters of credit		$ 0
Debt, weighted average interest rate		4.94%	2.60%
Interest Expense, Debt		$ 68,566,000	$ 52,551,000	$ 41,803,000
Interest Costs Capitalized		17,200,000	22,200,000	$ 30,200,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		1,395,000,000
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
Number of vessels pledged as collateral | vessel	3
Number of vessels removed as collateral | vessel	2
Number of drillships unencumbered | drillship	2
Outstanding credit facility		780,000,000	$ 1,030,000,000
Long-term line of credit, remaining borrowing capacity		615,000,000
Revolving Credit Facility [Member] | Junior Lien [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 400,000,000
Revolving Credit Facility [Member] | Eurodollar [Member] | Minimum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.50%
Unused capacity commitment fee	1.00%
Revolving Credit Facility [Member] | Eurodollar [Member] | Maximum [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	3.25%
Unused capacity commitment fee	1.30%
Revolving Credit Facility [Member] | Revolving Credit Facility, Maturing May 2018 [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		275,000,000
Revolving Credit Facility [Member] | Revolving Credit Facility, Maturing May 2019 [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 1,120,000,000