Segment and Geographic Information - Narrative (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	8 Months Ended	9 Months Ended		12 Months Ended
	Jun. 30, 2022	May 16, 2022	Jun. 30, 2022	Jun. 30, 2021	Sep. 30, 2021	Sep. 30, 2020
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			$ 405,296		$ 300,640	$ 130,495
Operating Income (Loss)			36,157	$ (46,555)	(60,439)	(18,060)
Assets	$ 14,969,922		14,969,922		2,116,756	335,651
Property, equipment and leasehold improvements, net	17,148		17,148		14,744	6,578
Gross profit			248,900	104,135	137,630	79,605
Net income	66,369	$ (13,223)	53,146	(9,406)	(20,608)	(20,317)
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest			39,961	(50,398)	(65,913)	(22,445)
Total Revenue			405,296	223,625	300,640	130,495
Total cost of revenue			156,396	119,490	163,010	50,890
Operating Expenses			212,743	150,690	198,069	97,665
Other income (expense), net			(310)	(4,000)	(5,359)	(4,335)
Interest (expense)				157
(Benefit) for income taxes			$ (13,185)	$ (40,992)	$ (45,305)	$ (2,128)
Basic (in dollars per share)			$ 1.30	$ (0.26)	$ (0.57)	$ (0.56)
Earnings Per Share, Diluted			$ 1.30	$ (0.26)	$ (0.57)	$ (0.56)
Basic (in shares)			40,931	36,308	36,308	36,308
Diluted (in shares)			41,008	36,308	36,308	36,308
OSI Inc.
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			$ 143,214		$ 173,252	$ 0
Operating Income (Loss)			(23,460)		(57,876)	0
Assets	1,762,915		1,762,915		1,805,001	0
SSE
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			88,272		127,388	130,495
Operating Income (Loss)			(3,864)		(2,563)	(18,060)
Assets	279,557		279,557		311,755	335,651
Heritage AspenTech
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			173,810		0	0
Operating Income (Loss)			63,481		0	0
Assets	12,927,450		12,927,450		0	0
License [Member]
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			278,589		180,914	42,038
Total cost of revenue			125,258		125,181	17,462
License [Member] | OSI Inc.
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			106,704		134,797	0
License [Member] | SSE
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			27,213		46,117	42,038
License [Member] | Heritage AspenTech
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			144,672		0	0
Maintenance
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			103,786		92,562	65,591
Total cost of revenue			15,030		18,610	16,092
Maintenance | OSI Inc.
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			30,971		31,777	0
Maintenance | SSE
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			47,542		60,785	65,591
Maintenance | Heritage AspenTech
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			25,273		0	0
Services and other
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			22,921		27,164	22,866
Total cost of revenue			16,108		19,219	17,336
Services and other | OSI Inc.
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			5,539		6,678	0
Services and other | SSE
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			13,517		20,486	22,866
Services and other | Heritage AspenTech
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			3,865		0	0
United States
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			173,500		123,200	18,500
Property, equipment and leasehold improvements, net	13,000		13,000		10,500	3,600
Americas
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			234,383		182,314	39,705
Property, equipment and leasehold improvements, net	14,591		14,591		11,819	4,322
Americas | OSI Inc.
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			117,289		149,853	0
Americas | SSE
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			27,982		32,461	39,705
Americas | Heritage AspenTech
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			89,112		0	0
Europe
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			84,958		58,026	49,294
Property, equipment and leasehold improvements, net	1,403		1,403		1,532	1,488
Europe | OSI Inc.
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			12,212		6,358	0
Europe | SSE
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			24,936		51,668	49,294
Europe | Heritage AspenTech
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			47,810		0	0
Asia, Middle East and Africa
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			85,955		60,300	41,496
Property, equipment and leasehold improvements, net	$ 1,154		1,154		1,393	768
Asia, Middle East and Africa | OSI Inc.
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			13,713		17,041	0
Asia, Middle East and Africa | SSE
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			35,354		43,259	41,496
Asia, Middle East and Africa | Heritage AspenTech
Geographic Information
Revenue from Contract with Customer, Excluding Assessed Tax			$ 36,888		$ 0	$ 0