Related Parties - Narrative (Details) $ in Millions						1 Months Ended		3 Months Ended			6 Months Ended		12 Months Ended
	Jul. 06, 2020 USD ($) shares	Jun. 30, 2020 USD ($) shares	Jan. 01, 2020	Feb. 08, 2019 USD ($)	Aug. 08, 2018 USD ($) shares	Jun. 30, 2020 USD ($)	Feb. 07, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($) profitInterestUnit	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Aug. 31, 2019
Related Party Transaction [Line Items]
IPO related expenses					$ 21.6
Total compensation expense for stock options granted							$ 11.7	$ 25.1	$ 3.7		$ 28.9	$ 4.2
Gross proceeds from sale of stock					$ 1,028.4
Stock option
Related Party Transaction [Line Items]
Total compensation expense for stock options granted								20.0			20.0
Common Stock
Related Party Transaction [Line Items]
Stock issued (shares) | shares					314,494,968
Subsequent Event
Related Party Transaction [Line Items]
IPO related expenses	$ 42.3
Stock issued (shares) | shares	108,506,312
Gross proceeds from sale of stock	$ 2,381.0
Subsequent Event | 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%
Stock Issuance Costs | Star Parent, L.P. | Subsequent Event
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 30.0
Board of Directors Chairman & Director | Stock option
Related Party Transaction [Line Items]
Total compensation expense for stock options granted		$ 20.0
Board of Directors Chairman & Director | Class B Profits Interest Units
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"												17.3
Number of Profit Interest Units Granted | profitInterestUnit										6,817.7428
Board of Directors Chairman & Director | Class C Profits Interest Units
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"										$ 37.9
Number of Profit Interest Units Granted | profitInterestUnit										15,867.8087
Board of Directors Chairman
Related Party Transaction [Line Items]
Stock options granted during period (shares) | shares		2,080,000
Board of Directors Chairman | Bilcar | Subsequent Event
Related Party Transaction [Line Items]
IPO related expenses	2.5
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 | Services Agreement with MVB Management, LLC and THL Managers VIII, LLC
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"										$ 29.1	0.0	0.0
Board of Directors Chairman | Stock Issuance Costs | Bilcar | Subsequent Event
Related Party Transaction [Line Items]
Expenses from transactions with related party	2.5
Board of Directors Chairman | Equity Commitment Fee | Cannae Holdings
Related Party Transaction [Line Items]
Expenses from transactions with related party				$ 12.0
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
Director
Related Party Transaction [Line Items]
Stock options granted during period (shares) | shares		2,080,000
Director | CC Star Holdings, LP | Subsequent Event
Related Party Transaction [Line Items]
IPO related expenses	2.5
Director | Stock Issuance Costs | CC Star Holdings, LP | Subsequent Event
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 2.5
Management | IPO Transaction
Related Party Transaction [Line Items]
Due to related parties		$ 0.5				$ 0.5		0.5			0.5
Management | Travel Costs
Related Party Transaction [Line Items]
Fees/ expenses with related party included in "Selling and Administrative Expenses"								0.1	$ 0.2		0.4	$ 0.2
Affiliated Entity | Subsequent Event | 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 | THL Managers | Subsequent Event
Related Party Transaction [Line Items]
IPO related expenses	$ 2.5
Affiliated Entity | Star Parent, L.P. | Subsequent Event
Related Party Transaction [Line Items]
IPO related expenses	30.0
Affiliated Entity | Cannae Holdings | Subsequent Event | Common Stock | Private Placement
Related Party Transaction [Line Items]
Gross proceeds from sale of stock	200.0
Affiliated Entity | Black Knight Inc. | Subsequent Event | Common Stock | Private Placement
Related Party Transaction [Line Items]
Gross proceeds from sale of stock	100.0
Affiliated Entity | CC Capital | Subsequent Event | Common Stock | Private Placement
Related Party Transaction [Line Items]
Gross proceeds from sale of stock	100.0
Affiliated Entity | Stock Issuance Costs | THL Managers | Subsequent Event
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 2.5
Affiliated Entity | Equity Commitment Fee | THL Managers
Related Party Transaction [Line Items]
Expenses from transactions with related party				7.5
Chief Operating Officer | Motive Partners | London
Related Party Transaction [Line Items]
Term of lease														5 years
Chief Operating Officer | Motive Partners | New York
Related Party Transaction [Line Items]
Term of lease													1 year
Chief Operating Officer | Due Diligence Consulting Services Fee | Motive Partners
Related Party Transaction [Line Items]
Expenses from transactions with related party				$ 0.6
Chief Operating Officer | Lease Cost | Motive Partners | London
Related Party Transaction [Line Items]
Expenses from transactions with related party								$ 0.5			$ 1.1
Chief Operating Officer | Lease Cost | Motive Partners | New York
Related Party Transaction [Line Items]
Expenses from transactions with related party													$ 0.2
Chief Operating Officer | Lease Termination Fee | Motive Partners | London
Related Party Transaction [Line Items]
Expenses from transactions with related party						$ 0.1