Derivative Instruments and Hedging Activities (Details) (USD $)	Mar. 31, 2013	Sep. 30, 2012
Derivative instruments and hedging activities
Estimated unrealized net gains (losses) from cash flow hedges which are expected to be reclassified into earnings in the next twelve months	$ 2,600,000
Forward starting swap
Derivative instruments and hedging activities
Notional Principal outstanding derivative instruments	58,400,000
Instruments designated as accounting hedges: | Foreign currency forwards
Derivative instruments and hedging activities
Notional Principal outstanding derivative instruments	380,823,000	382,500,000
Instruments designated as accounting hedges: | Forward starting swap
Derivative instruments and hedging activities
Notional Principal outstanding derivative instruments	58,415,000	58,415,000
Instruments not designated as accounting hedges: | Foreign currency forwards
Derivative instruments and hedging activities
Notional Principal outstanding derivative instruments	$ 7,430,000	$ 5,945,000