Segment Information - Summary of Segment Information (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2025 USD ($) Segment	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | Segment	2
Segment revenues:
Total revenues	$ 1,990,869	$ 1,717,526	$ 1,513,557
Expenses	(1,066,019)	(983,897)	(870,727)
Operating income	924,850	733,629	642,830
Unallocated share-based compensation expense	(156,667)	(149,439)	(123,847)
Unallocated amortization expense	0	(917)	(1,100)
Unallocated restructuring charges	10,922	0	0
Unallocated interest expense, net	(133,647)	(105,638)	(95,546)
Unallocated other income, net	11,392	14,034	6,340
Income before income taxes	802,595	642,025	553,624
Scores
Segment revenues:
Total revenues	1,168,575	919,650	773,828
Software
Segment revenues:
Total revenues	822,294	797,876	739,729
Operating Segments
Segment revenues:
Expenses	(716,932)	(646,643)	(591,295)
Operating income	1,273,937	1,070,883	922,262
Operating Segments | Scores
Segment revenues:
Total revenues	1,168,575	919,650	773,828
Expenses	(142,332)	(106,296)	(92,757)
Operating income	1,026,243	813,354	681,071
Operating Segments | Software
Segment revenues:
Total revenues	822,294	797,876	739,729
Expenses	(574,600)	(540,347)	(498,538)
Operating income	247,694	257,529	241,191
Unallocated corporate
Segment revenues:
Expenses	(181,498)	(186,898)	(156,426)
On-premises and SaaS software
Segment revenues:
Total revenues	740,145	711,340	640,182
On-premises and SaaS software | Software
Segment revenues:
Total revenues	740,145	711,340	640,182
On-premises and SaaS software | Operating Segments | Scores
Segment revenues:
Total revenues	0	0	0
On-premises and SaaS software | Operating Segments | Software
Segment revenues:
Total revenues	740,145	711,340	640,182
Professional services
Segment revenues:
Total revenues	82,149	86,536	99,547
Professional services | Operating Segments | Scores
Segment revenues:
Total revenues	0	0	0
Professional services | Operating Segments | Software
Segment revenues:
Total revenues	82,149	86,536	99,547
Scores
Segment revenues:
Total revenues	1,168,575	919,650	773,828
Scores | Operating Segments | Scores
Segment revenues:
Total revenues	1,168,575	919,650	773,828
Scores | Operating Segments | Software
Segment revenues:
Total revenues	$ 0	$ 0	$ 0