Derivative Instruments and Hedging Activities - Notional principal amounts (Details) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 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	$ 171,629	$ 217,796
Not designated but designed to manage exposure: | Foreign currency forwards
Derivative Instruments and Hedging Activities
Notional principal outstanding derivative instruments	102,600	117,800
Instruments not designated as accounting hedges: | Foreign currency forwards
Derivative Instruments and Hedging Activities
Notional principal outstanding derivative instruments	$ 125,372	$ 142,820