Long-Term Debt (Narrative) (Details) (USD $)	9 Months Ended			1 Months Ended	9 Months Ended		9 Months Ended			9 Months Ended
	Jun. 30, 2012	Jun. 30, 2012 2011 Credit Facility [Member]	Jun. 30, 2012 3.4% Interest Rate Swaps Due 2014 [Member] Swap	Jan. 31, 2012 Senior Notes [Member] 6.5% Senior Notes [Member]	Jun. 30, 2012 Senior Notes [Member] 6.5% Senior Notes [Member]	Sep. 30, 2011 Senior Notes [Member] 6.5% Senior Notes [Member]	Jun. 30, 2012 Line of Credit [Member] 2011 Credit Facility [Member] Y	Sep. 30, 2011 Line of Credit [Member] 2011 Credit Facility [Member]	Jun. 30, 2011 Line of Credit [Member] 2011 Credit Facility [Member]	Jun. 30, 2012 Line of Credit [Member] 2011 Credit Facility [Member] Maximum [Member]	Jun. 30, 2012 Line of Credit [Member] 2011 Credit Facility [Member] Minimum [Member]
Line of Credit Facility [Line Items]
Principal amount				$ 450,000,000	$ 450,000,000	$ 0
Debt instrument maturity year				2020
Interest rate				6.50%	6.50%
Net proceeds, after deducting underwriting discounts and estimated offering expenses				440,000,000
Indenture governing final judgments, maximum amount					50.0
Senior secured revolving credit facility term, in years							5
Credit facility capacity											750,000,000
Senior secured revolving credit facility, initiation date							May 2011
Credit facility variable rate							Eurodollar
Credit facility basis spread on variable rate							2.50%
Market adjustable interest rate (per annum)							3.30%	3.10%	3.10%
Incremental commitment increase										350,000,000
Commitment fees										1,100,000,000
2011 Credit Facility, description		interest at the Eurodollar rate plus a margin of 2.5% (approximately 3.3% per annum at June 30, 2012, after considering the impact of our interest rate swaps).
2011 Credit Facility, commitment fee (per annum)							1.00%
Number of Interest Rate Derivatives Held In Effect to Fix Interest Rate			3
Number of interest rate swap agreements	5		5
Outstanding credit facility borrowing	$ 150,000,000		$ 250,000,000				$ 205,000,000	$ 520,000,000
Interest rate fixed as result of interest rate swap hedges	3.50%		3.40%