Derivative Instruments and Hedging Activities (Details) (USD $)	Dec. 31, 2012	Sep. 30, 2012
Derivative instruments and hedging activities
Estimated unrealized net gains from cash flow hedges which are expected to be reclassified into earnings in the next twelve months	$ 1,900,000
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	393,902,000	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	$ 8,511,000	$ 5,945,000