Derivative Instruments and Hedging Activities - Fair value of derivative financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016
Derivative Instruments and Hedging Activities
Asset derivatives	$ 5,623	$ 15,970
Liability derivatives	5,216	15,085
Foreign currency forwards | Other current assets
Derivative Instruments and Hedging Activities
Asset derivatives	4,472	14,769
Foreign currency forwards | Other noncurrent assets
Derivative Instruments and Hedging Activities
Asset derivatives	1,151	1,201
Foreign currency forwards | Other current liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	4,065	13,752
Foreign currency forwards | Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	$ 1,151	$ 1,333