Derivative Instruments and Hedging Activities - Fair value of derivative financial instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Derivative Instruments and Hedging Activities
Asset derivatives	$ 2,803	$ 3,494
Liability derivatives	2,127	757
Foreign currency forwards | Other current assets
Derivative Instruments and Hedging Activities
Asset derivatives	930	2,635
Foreign currency forwards | Other assets
Derivative Instruments and Hedging Activities
Asset derivatives	469	619
Foreign currency forwards | Other current liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	1,855	529
Foreign currency forwards | Other noncurrent liabilities
Derivative Instruments and Hedging Activities
Liability derivatives	272	228
Forward starting swap | Other assets
Derivative Instruments and Hedging Activities
Asset derivatives	$ 1,404	$ 240