Derivative Instruments and Hedging Activities - Fair value of derivative financial instruments (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Sep. 30, 2016
Derivative Instruments and Hedging Activities
Asset derivatives	$ 2,782	$ 15,970
Liability derivatives	3,221	15,085
Foreign currency forwards | Other current assets
Derivative Instruments and Hedging Activities
Asset derivatives	1,961	14,769
Foreign currency forwards | Other noncurrent assets
Derivative Instruments and Hedging Activities
Asset derivatives	821	1,201
Foreign currency forwards | Other current liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	2,400	13,752
Foreign currency forwards | Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	$ 821	$ 1,333