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Credit Facilities and Debt Credit Facilities and Debt - 5.375% Senior Notes due 2020 (Details) - USD ($) $ in Thousands	2 Months Ended	3 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Oct. 22, 2012	Aug. 14, 2012
Debt Instrument [Line Items]
Gain (Loss) on Extinguishment of Debt			$ (910)	$ 348	$ (18,565)
Long-term Debt		$ 2,185,361	1,936,406	2,185,361
5.375% Senior Notes due August 15, 2020
Debt Instrument [Line Items]
Repayments of Debt		$ 150,000	600,000
Gain (Loss) on Extinguishment of Debt			300	$ 18,600
Long-term Debt			300,000
Proceeds from issuance of senior notes	$ 689,100		$ 351,700
Debt Instrument, Interest Rate, Effective Percentage		5.375%	5.375%	5.375%
Unamortized Debt Issuance Expense		$ 1,200	$ 0	$ 1,200
5.375% Senior Notes due 2020		$ 298,759	$ 0	$ 298,759		$ 350,000	$ 700,000
Senior notes, stated interest rate		5.375%	5.375%	5.375%		5.375%
Term Loan Facility Due August Seventh Twenty Ninteen [Member]
Debt Instrument [Line Items]
Repayments of Debt				$ 472,500