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Related Parties - Narrative (Details) $ / shares in Units, $ in Millions				1 Months Ended		3 Months Ended		6 Months Ended
	Jul. 06, 2020 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) shares	Jan. 01, 2020	Jun. 30, 2021 USD ($) director	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) director	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) director shares	Jun. 30, 2020 USD ($)	Aug. 31, 2019
Related Party Transaction [Line Items]
Stock options granted during period (shares) \| shares								0
Total compensation expense for stock options granted						$ 7.1	$ 25.1	$ 14.7	$ 28.9
Consideration received on transaction	$ 2,381.0
Private Placement
Related Party Transaction [Line Items]
Stock issued (shares) \| shares	18,458,700
Offering price (USD per share) \| $ / shares	$ 21.67
IPO
Related Party Transaction [Line Items]
Stock issued (shares) \| shares	90,047,612
Offering price (USD per share) \| $ / shares	$ 22.00
Stock options
Related Party Transaction [Line Items]
Total compensation expense for stock options granted						$ (0.4)	20.0	$ 1.1	20.0
Stock Issuance Costs \| Star Parent, L.P.
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 30.0
Affiliated Entity
Related Party Transaction [Line Items]
Number of directors designated by related parties \| director				5		5		5
Affiliated Entity \| Common Stock \| Private Placement
Related Party Transaction [Line Items]
Stock issued (shares) \| shares	18,458,700
Issuance price per share relative to IPO price per share (as a percent)	98.50%
Affiliated Entity \| Black Knight Inc. \| Common Stock \| Private Placement
Related Party Transaction [Line Items]
Consideration received on transaction	$ 100.0
Affiliated Entity \| Cannae Holdings \| Common Stock \| Private Placement
Related Party Transaction [Line Items]
Consideration received on transaction	200.0
Affiliated Entity \| CC Capital \| Common Stock \| Private Placement
Related Party Transaction [Line Items]
Consideration received on transaction	$ 100.0
Affiliated Entity \| Strategic Partnership Agreement \| Black Knight Inc.
Related Party Transaction [Line Items]
Term of strategic partnership				5 years
Revenue from related parties				$ 24.0		$ 3.2		$ 3.2
Expenses from transactions with related party				$ 34.0
Affiliated Entity \| Consulting Service Agreement \| Black Knight Inc.
Related Party Transaction [Line Items]
Expenses from transactions with related party								$ 0.2
Mark-up on consulting services (as a percent)				10.00%		10.00%		10.00%
Chief Operating Officer \| Motive Partners \| London
Related Party Transaction [Line Items]
Term of lease										5 years
Chief Operating Officer \| Lease Termination Fee \| Motive Partners \| London
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"					$ 0.1
Chief Operating Officer \| Lease Cost \| Motive Partners \| London
Related Party Transaction [Line Items]
Expenses from transactions with related party							0.5		1.1
Management \| Travel Costs
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"						$ 0.1		$ 0.1	0.4
Management \| IPO Transaction Service Fees
Related Party Transaction [Line Items]
Due to related parties		$ 0.5			$ 0.5		0.5		0.5
Board of Directors Chairman
Related Party Transaction [Line Items]
Stock options granted during period (shares) \| shares		2,080,000
Board of Directors Chairman \| Trasimene Capital Management, LLC
Related Party Transaction [Line Items]
Term of service agreement			3 years
Transaction fee valuation rate (as a percent)			1.00%
Board of Directors Chairman \| Service Agreement, Transaction Fees \| Trasimene Capital Management, LLC
Related Party Transaction [Line Items]
Expenses from transactions with related party							$ 0.4		$ 0.4
Director
Related Party Transaction [Line Items]
Stock options granted during period (shares) \| shares		2,080,000
Board of Directors Chairman & Director \| Stock options
Related Party Transaction [Line Items]
Total compensation expense for stock options granted		$ 20.0