Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Basic:
Net earnings attributable to Black Knight	$ 168.5	$ 182.3	$ 45.8
Shares used for basic net earnings per share:
Weighted average shares of Class A common stock outstanding (in shares)	147.6	88.7	65.9
Basic net earnings per share (in dollars per share)	$ 1.14	$ 2.06	$ 0.69
Diluted:
Earnings before income taxes	$ 206.2	$ 192.4	$ 158.8
Income tax benefit excluding the effect of noncontrolling interests		(32.2)
Net earnings		$ 224.6
Shares used for diluted net earnings per share:
Weighted average shares of Class A common stock outstanding (in shares)	147.6	88.7	65.9
Weighted average shares of Class A common stock, diluted (in shares)	148.2	152.4	67.9
Diluted net earnings per share (in dollars per share)	$ 1.14	$ 1.47	$ 0.67
Common Class A
Shares used for basic net earnings per share:
Weighted average shares of Class A common stock outstanding (in shares)	147.6	88.7	65.9
Shares used for diluted net earnings per share:
Weighted average shares of Class A common stock outstanding (in shares)	147.6	88.7	65.9
Dilutive effect of unvested restricted shares of Class A common stock (in shares)	0.6	0.6	2.0
Common Class B
Shares used for basic net earnings per share:
Weighted average shares of Class A common stock outstanding (in shares)	0.0	63.1	0.0
Shares used for diluted net earnings per share:
Weighted average shares of Class A common stock outstanding (in shares)	0.0	63.1	0.0