Derivative Instruments and Hedging Activities - Fair value of derivative financial instruments (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Derivative Instruments and Hedging Activities
Asset derivatives	$ 3,305	$ 15,970
Liability derivatives	3,942	15,085
Foreign currency forwards | Other current assets
Derivative Instruments and Hedging Activities
Asset derivatives	2,459	14,769
Foreign currency forwards | Other noncurrent assets
Derivative Instruments and Hedging Activities
Asset derivatives	846	1,201
Foreign currency forwards | Other current liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	3,096	13,752
Foreign currency forwards | Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	$ 846	$ 1,333