Derivative Instruments and Hedging Activities - Fair value of derivative financial instruments (Details) - Instruments designated as accounting hedges: - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Foreign currency forwards
Derivative Instruments and Hedging Activities
Asset derivatives	$ 3,494	$ 2,117
Liability derivatives	757	1,732
Foreign currency forwards | Other current assets
Derivative Instruments and Hedging Activities
Asset derivatives	2,635	1,803
Foreign currency forwards | Other assets
Derivative Instruments and Hedging Activities
Asset derivatives	619	314
Foreign currency forwards | Other current liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	529	1,657
Foreign currency forwards | Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	228	$ 75
Interest Rate Swaps | Other assets
Derivative Instruments and Hedging Activities
Asset derivatives	$ 240