Derivative Instruments and Hedging Activities (Details) - Foreign currency forwards - USD ($) $ in Thousands	Dec. 31, 2015	Sep. 30, 2015
Instruments designated as accounting hedges:
Derivative Instruments and Hedging Activities
Notional principal outstanding derivative instruments	$ 189,932	$ 217,796
Not designated but designed to manage exposure:
Derivative Instruments and Hedging Activities
Notional principal outstanding derivative instruments	117,000	117,800
Instruments not designated as accounting hedges:
Derivative Instruments and Hedging Activities
Notional principal outstanding derivative instruments	$ 144,326	$ 142,820