Segment Information - Summary of Segment Information (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2024 USD ($) Segment	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | Segment	2
Segment revenues:
Revenue	$ 1,717,526	$ 1,513,557	$ 1,377,270
Segment operating expense	(983,897)	(870,727)	(834,856)
Operating income	733,629	642,830	542,414
Unallocated share-based compensation expense	(149,439)	(123,847)	(115,355)
Unallocated amortization expense	(917)	(1,100)	(2,061)
Unallocated interest expense, net	(105,638)	(95,546)	(68,967)
Unallocated other income (expense), net	14,034	6,340	(2,138)
Depreciation and amortization	9,398	10,106	15,242
Gain (Loss) on Disposition of Business	0	1,941	0
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	642,025	553,624	471,309
Software
Segment revenues:
Revenue	797,876	739,729	670,627
Scores
Segment revenues:
Revenue	919,650	773,828	706,643
Operating Segments
Segment revenues:
Revenue	1,717,526	1,513,557	1,377,270
Segment operating expense	(833,541)	(747,721)	(717,440)
Operating income	883,985	765,836	659,830
Operating Segments | Software
Segment revenues:
Revenue	797,876	739,729	670,627
Segment operating expense	(540,347)	(498,538)	(487,505)
Operating income	257,529	241,191	183,122
Depreciation and amortization	8,881	9,550	14,412
Operating Segments | Scores
Segment revenues:
Revenue	919,650	773,828	706,643
Segment operating expense	(106,296)	(92,757)	(87,288)
Operating income	813,354	681,071	619,355
Depreciation and amortization	451	485	723
Unallocated Corporate Expenses
Segment revenues:
Segment operating expense	(186,898)	(156,426)	(142,647)
Operating income	(186,898)	(156,426)	(142,647)
Depreciation and amortization	66	71	107
On-premises and SaaS software
Segment revenues:
Revenue	711,340	640,182	564,751
On-premises and SaaS software | Operating Segments
Segment revenues:
Revenue	711,340	640,182	564,751
On-premises and SaaS software | Operating Segments | Software
Segment revenues:
Revenue	711,340	640,182	564,751
On-premises and SaaS software | Operating Segments | Scores
Segment revenues:
Revenue	0	0	0
Professional services
Segment revenues:
Revenue	86,536	99,547	105,876
Professional services | Operating Segments
Segment revenues:
Revenue	86,536	99,547	105,876
Professional services | Operating Segments | Software
Segment revenues:
Revenue	86,536	99,547	105,876
Professional services | Operating Segments | Scores
Segment revenues:
Revenue	0	0	0
Scores Products
Segment revenues:
Revenue	919,650	773,828	706,643
Scores Products | Operating Segments
Segment revenues:
Revenue	919,650	773,828	706,643
Scores Products | Operating Segments | Software
Segment revenues:
Revenue	0	0	0
Scores Products | Operating Segments | Scores
Segment revenues:
Revenue	$ 919,650	$ 773,828	$ 706,643