Revenue from Contracts with Customers - Disaggregated Revenue (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2021 USD ($) customer	Sep. 30, 2020 USD ($) customer	Sep. 30, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Revenue	$ 1,316,536	$ 1,294,562	$ 1,160,083
Revenue from Contract with Customer Benchmark | Geographic Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	100.00%	100.00%	100.00%
Revenue from Contract with Customer Benchmark | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk, number of customers | customer	3	1
Accounts Receivable | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration risk, number of customers | customer	1	0
Scores
Disaggregation of Revenue [Line Items]
Revenue	$ 654,147	$ 528,547	$ 421,177
Software
Disaggregation of Revenue [Line Items]
Revenue	$ 662,389	$ 766,015	$ 738,906
TransUnion Equifax and Experian customers | Revenue from Contract with Customer Benchmark | Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	38.00%	33.00%	29.00%
On-Premises Software
Disaggregation of Revenue [Line Items]
Revenue	$ 266,452	$ 347,532	$ 342,848
On-Premises Software | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	51.00%	59.00%	62.00%
SaaS Software
Disaggregation of Revenue [Line Items]
Revenue	$ 251,436	$ 237,044	$ 214,120
SaaS Software | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	49.00%	41.00%	38.00%
On-premises and SaaS software
Disaggregation of Revenue [Line Items]
Revenue	$ 517,888	$ 584,576	$ 556,968
On-premises and SaaS software | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	100.00%	100.00%	100.00%
On-premises and SaaS software | Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Revenue	$ 59,024	$ 127,666	$ 111,308
On-premises and SaaS software | Transferred at Point in Time | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	11.00%	22.00%	20.00%
On-premises and SaaS software | Transferred over Time
Disaggregation of Revenue [Line Items]
Revenue	$ 458,864	$ 456,910	$ 445,660
On-premises and SaaS software | Transferred over Time | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	89.00%	78.00%	80.00%
Platform Software
Disaggregation of Revenue [Line Items]
Revenue	$ 66,884	$ 65,665	$ 39,175
Platform Software | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	13.00%	11.00%	7.00%
Non-Platform Software
Disaggregation of Revenue [Line Items]
Revenue	$ 451,004	$ 518,911	$ 517,793
Non-Platform Software | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	87.00%	89.00%	93.00%
Business-to-business Scores
Disaggregation of Revenue [Line Items]
Revenue	$ 446,538	$ 381,929	$ 302,103
Business-to-business Scores | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	68.00%	72.00%	72.00%
Business-to-consumer Scores
Disaggregation of Revenue [Line Items]
Revenue	$ 207,609	$ 146,618	$ 119,074
Business-to-consumer Scores | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	32.00%	28.00%	28.00%
Scores Products
Disaggregation of Revenue [Line Items]
Revenue	$ 654,147	$ 528,547	$ 421,177
Scores Products | Revenue from Contract with Customer Benchmark | Product Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	100.00%	100.00%	100.00%
Americas
Disaggregation of Revenue [Line Items]
Revenue	$ 1,049,933	$ 992,225	$ 872,452
Americas | Revenue from Contract with Customer Benchmark | Geographic Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	80.00%	76.00%	75.00%
Americas | Scores
Disaggregation of Revenue [Line Items]
Revenue	$ 633,497	$ 514,909	$ 409,369
Americas | Software
Disaggregation of Revenue [Line Items]
Revenue	416,436	477,316	463,083
EMEA
Disaggregation of Revenue [Line Items]
Revenue	$ 190,396	$ 203,584	$ 195,186
EMEA | Revenue from Contract with Customer Benchmark | Geographic Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	14.00%	16.00%	17.00%
EMEA | Scores
Disaggregation of Revenue [Line Items]
Revenue	$ 11,881	$ 6,385	$ 6,359
EMEA | Software
Disaggregation of Revenue [Line Items]
Revenue	178,515	197,199	188,827
Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue	$ 76,207	$ 98,753	$ 92,445
Asia Pacific | Revenue from Contract with Customer Benchmark | Geographic Concentration Risk
Disaggregation of Revenue [Line Items]
Concentration Risk, Percentage	6.00%	8.00%	8.00%
Asia Pacific | Scores
Disaggregation of Revenue [Line Items]
Revenue	$ 8,769	$ 7,253	$ 5,449
Asia Pacific | Software
Disaggregation of Revenue [Line Items]
Revenue	$ 67,438	$ 91,500	$ 86,996