Revenue from Contracts with Customers - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Change in Contract with Customer, Asset [Roll Forward]
Balance, beginning of year	$ 132,492	$ 0
Impacts from adoption of ASC 606	0	57,499
Revenue recognized during period but not yet billed	37,260	27,459
Contract asset net additions	123,533	88,068
Contract assets acquired through the purchase of Shape	6,045	0
Contract assets reclassified to accounts receivable	(98,858)	(40,534)
Balance, end of year	200,472	132,492
Change in Contract with Customer, Liability [Roll Forward]
Balance, beginning of year	1,198,116	1,015,321
Impacts from adoption of ASC 606	0	68,078
Amounts billed but not recognized as revenues	850,022	866,142
Amounts acquired through the purchase of Shape	39,000	0
Revenues recognized related to the opening balance of deferred revenue	(814,506)	(751,425)
Balance, end of year	$ 1,272,632	$ 1,198,116