Equity-based Compensation - Narrative (Details) $ / shares in Units, $ in Millions				1 Months Ended		3 Months Ended				5 Months Ended	9 Months Ended
	Dec. 31, 2020	Jun. 08, 2020 USD ($) $ / shares shares	Mar. 31, 2020	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) grantee	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 07, 2020	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($) shares	May 27, 2020 shares	Nov. 30, 2019	Dec. 31, 2018 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity award conversion, incremental grant date fair value | $		$ 4.0
Award vesting period											4 years
Cash distributions | $											$ 9.9	$ 16.5
Number of units with accelerated vesting											4
Additional expense recognized attributable to service period already elapsed | $						$ 28.4		$ 5.5			$ 104.2	$ 17.1
Class A common stock | IPO
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Public offering price (in dollars per share) | $ / shares		$ 21.00
2020 Omnibus Incentive Plan | Class A common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Units authorized (in shares)													18,650,000
2020 Omnibus Incentive Plan | Class A common stock | Forecast
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase to authorized plan shares based on stock outstanding, percentage	5.00%
Pre-IPO Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period										4 years
Pre-IPO Awards | Tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period										2 years
Award vesting percentage										50.00%
Post-IPO Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period				4 years
Post-IPO Awards | Tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage				25.00%
Post-IPO Awards | Quarterly vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting percentage				6.25%
Exercise of Class A Common Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in conversion (in shares)		576,708
Exercise of Class A Common Stock Options | Class A common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in conversion (in shares)											576,708
HoldCo Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued in conversion (in shares)		1,325,330									1,332,239
Class P Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares converted (in shares)		(1,950,930)									(1,950,930)	0
Class 1 Unit | Class A common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Economic equivalent of Unit (in shares)											1
HSKB Incentive Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance vesting condition (more than) (as a percent)														90.00%
Number of grantees affected | grantee					142
Increase in unrecognized equity-based compensation cost | $					$ 88.4
Cash distributions | $									$ 21.8		$ 11.3
Amount allocated to be paid if holder of grant remains employed | $				$ 5.3		$ 12.2	$ 5.3				$ 12.2				$ 31.3
Employment period			4 years						3 years
HSKB Incentive Units | Tranche one
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					2 years
Award vesting percentage					50.00%
HSKB Phantom Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional expense recognized attributable to service period already elapsed | $							$ 57.6
HSKB Phantom Units | ZoomInfo OpCo and HSKB 2019 Phantom Unit Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Period to settle awards					30 days
HSKB Phantom Units | ZoomInfo OpCo and HSKB 2019 Phantom Unit Plans | Common Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Economic equivalent of Unit (in shares)											1