Revenue (Contract Assets and Liabilities) (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Contract liabilities	$ 36,894	$ 33,691	$ 26,259	$ 39,051
Change in Contract with Customer, Asset [Roll Forward]
beginning of period	80,759	73,467
Recognized in current period	147,593	172,228
Reclassified to accounts receivable	153,964	166,535
Amounts related to sale of the Memcor product line	0	2,710
Foreign currency	413	(621)
end of period	74,801	81,249
Change in Contract with Customer, Liability [Roll Forward]
Recognized in current period	158,452	157,114
Amounts in beginning balance reclassified to revenue	(20,703)	(37,497)
Current period amounts reclassified to revenue	(127,684)	(124,194)
Amounts related to sale of the Memcor product line	0	(700)
Foreign currency	$ 570	$ (83)