Debt Credit Facility - Narrative (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)
Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,550,000		$ 1,550,000
Maximum Leverage Ratio Through December 2017	4.50		4.50
Maximum Leverage Ratio After December 2017	4.00		4.00
Long-term line of credit	$ 1,060,000		$ 1,060,000
Weighted average interest rate	2.01%		2.01%
Interest costs capitalized	$ 6,081	$ 6,700	$ 14,917	$ 22,900
Remaining borrowing capacity	484,000		$ 484,000
Revolving Credit Facility | Minimum | Eurodollar
Line of Credit Facility [Line Items]
Basis spread on variable rate			1.75%
Unused capacity commitment fee			0.30%
Revolving Credit Facility | Maximum | Eurodollar
Line of Credit Facility [Line Items]
Basis spread on variable rate			2.00%
Unused capacity commitment fee			0.40%
Letter of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding	6,300		$ 6,300
May 2019 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,245,000		1,245,000
May 2018 | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 305,000		$ 305,000