Long-term Debt (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009
Debt financing costs	$ 0	$ 0	$ 5,892
Amortization of debt financing costs recognized as interest expense	764	1,515	2,031
Balance of unamortized debt financing costs	2,153	2,917
Designated as Hedging Instrument [Member] | Current and Long-Term Debt [Member]
Realized Gain (Loss) On Terminated Derivatives, Current Portion	3	67
2008 Note Purchase Agreement [Member]
Leverage Ratio	3.5:1.0
Issuance Date	October 2008
Debt Covenant, Ratio Of Consolidated Net Debt to Debt Covenant EBITDA	3.5:1.0
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value	425,000
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Income	50.00%
Debt Covenant, Calculations, Period Of Time	rolling four quarter basis
Cross default provisions related to the Company's other outstanding debt arrangements in excess of this amount, the occurrence of which would permit the lenders to accelerate the amounts due thereunder	25,000
Debt Covenant, Ratio Of Consolidated Net Debt to Debt Covenant EBITDA During Material Acquisition Period, Maximum	4.0:1.0
Debt Covenant, Maximum Percentage of Priority Debt To Consolidated Net Worth	20.00%
2009 Note Purchase Agreement [Member]
Issuance Date	April 2009
Debt Covenant, Ratio Of Consolidated Net Debt to Debt Covenant EBITDA	3.5:1.0
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value	485,940
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Income	50.00%
Debt Covenant, Calculations, Period Of Time	rolling four quarter basis
Cross default provisions related to the Company's other outstanding debt arrangements in excess of this amount, the occurrence of which would permit the lenders to accelerate the amounts due thereunder	30,000
Debt Covenant, Maximum Percentage of Priority Debt To Consolidated Net Worth	20.00%
The Notes [Member]
Prepayment, Maximum Percentage of Principal	100.00%
Prepayment, Partial Payment Minimum	1,000
Prepayment, Make-Whole Amount Computation, Discount Rate Basis Points	50
Minimum [Member] | 2008 Term Loan [Member]
Basis Spread On Variable Rate	1.00%
Maximum [Member] | 2008 Term Loan [Member]
Basis Spread On Variable Rate	2.25%
2008 Term Loan [Member]
Issuance Date	October 2008
Face Amount	150,000
Option For Additonal Indebtedness	50,000
Variable Rate Basis	LIBOR
Principal Payment Amount	1,875
Frequency of Periodic Payment	quarterly
Debt Covenant, Ratio Of Consolidated Net Debt to Debt Covenant EBITDA	3.5:1.0
Debt Covenant, Minimum Consolidated Net Worth Calculation, Base Value	400,000
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Income	50.00%
Debt Covenant, Minimum Consolidated Net Worth Calculation, Percentage of Net Proceeds of Issuance of Capital Stock	50.00%
Debt Covenant, Calculations, Period Of Time	rolling four quarter basis
Cross default provisions related to the Company's other outstanding debt arrangements in excess of this amount, the occurrence of which would permit the lenders to accelerate the amounts due thereunder	$ 15,000