Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020	Sep. 30, 2019
Basic:
Net earnings attributable to Black Knight	$ 127.8		$ 37.3		$ 217.0	$ 95.9
Weighted average shares of common stock outstanding (in shares)	155.4	[1]	147.7	[1]	150.9	147.6
Basic net earnings per share (in dollars per share)	$ 0.82		$ 0.25		$ 1.44	$ 0.65
Shares used for diluted net earnings per share:
Weighted average shares of common stock outstanding (in shares)	155.4	[1]	147.7	[1]	150.9	147.6
Weighted average shares of common stock, diluted (in shares)	156.3	[1]	148.5	[1]	151.7	148.4
Diluted net earnings per share (in dollars per share)	$ 0.82		$ 0.25		$ 1.43	$ 0.65
Common Class A
Basic:
Weighted average shares of common stock outstanding (in shares)	155.4		147.7		150.9	147.6
Shares used for diluted net earnings per share:
Weighted average shares of common stock outstanding (in shares)	155.4		147.7		150.9	147.6
Dilutive effect of unvested restricted shares of Class A common stock (in share)	0.9		0.8		0.8	0.8

[1] Net of income tax expense of $1.6 million and $1.0 million for the three and nine months ended September 30, 2020, respectively, and income tax benefit of $1.1 million and $2.0 million for the three and nine months ended September 30, 2019, respectively.