Employee Stock Purchase Plan and 401(k) Plan - Stock Purchase Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jul. 20, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 50.9	$ 18.9	$ 12.4
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation expense	$ 7.8	$ 6.0	$ 5.8
Black Knight ESPP Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase plan (ESPP), annual contributions per employee (as a percent)				3.00%
Black Knight ESPP Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase plan (ESPP), annual contributions per employee (as a percent)				15.00%