Derivative Instruments and Hedging Activities (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2016	Sep. 30, 2015
Derivative Instruments and Hedging Activities
Term of derivative contract	3 years
Instruments designated as accounting hedges: | Foreign currency forwards
Derivative Instruments and Hedging Activities
Notional principal outstanding derivative instruments	$ 172,127	$ 217,796
Not designated but designed to manage exposure: | Foreign currency forwards
Derivative Instruments and Hedging Activities
Notional principal outstanding derivative instruments	126,000	117,800
Instruments not designated as accounting hedges: | Foreign currency forwards
Derivative Instruments and Hedging Activities
Notional principal outstanding derivative instruments	$ 153,137	$ 142,820