Derivative Instruments and Hedging Activities - Fair value of derivative financial instruments (Details) - Instruments designated as accounting hedges: - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Foreign currency forwards
Derivative Instruments and Hedging Activities
Asset derivatives	$ 1,620	$ 3,494
Liability derivatives	18,627	757
Foreign currency forwards | Other current assets
Derivative Instruments and Hedging Activities
Asset derivatives	1,398	2,635
Foreign currency forwards | Other assets
Derivative Instruments and Hedging Activities
Asset derivatives	222	619
Foreign currency forwards | Other current liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	4,557	529
Foreign currency forwards | Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	866	228
Forward starting swap | Other assets
Derivative Instruments and Hedging Activities
Asset derivatives		$ 240
Forward starting swap | Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	$ 13,204