Derivative Instruments and Hedging Activities - Fair value of derivative financial instruments (Details) - Instruments designated as accounting hedges: - Foreign currency forwards - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments and Hedging Activities
Asset derivatives	$ 2,117	$ 3,719
Liability derivatives	1,732	4,584
Other current assets
Derivative Instruments and Hedging Activities
Asset derivatives	1,803	2,591
Other noncurrent assets
Derivative Instruments and Hedging Activities
Asset derivatives	314	1,128
Other current liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	1,657	3,456
Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	$ 75	$ 1,128