Revenue from Contracts with Customers - Capitalized contract acquisition costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Changes In Capitalized Contract Cost [Roll Forward]
Beginning Balance			$ 59,446
Additional capitalized contract acquisition costs deferred			31,759
Amortization of capitalized contract acquisition costs	$ (7,800)	$ (6,900)	(24,768)	$ (21,300)
Ending Balance	$ 66,437		$ 66,437