Segment Information - Summarized Financial Information (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment			2
Revenues	$ 312.6	$ 299.1	$ 896.4	$ 877.1
Expenses:
Operating expenses	167.2	163.9	485.1	483.3
Transition and integration costs	21.9	0.4	26.8	2.3
EBITDA	123.5	134.8	384.5	391.5
Depreciation and amortization	64.0	59.6	180.3	174.0
Operating income (loss)	59.5	75.2	204.2	217.5
Interest expense	(14.7)	(16.5)	(42.4)	(48.2)
Other (expense) income, net	(0.9)	(0.1)	17.1	(0.9)
Earnings before income taxes and equity in earnings (losses) of unconsolidated affiliates	43.9	58.6	178.9	168.4
Income tax expense	15.9	9.4	41.3	34.6
Earnings before equity in earnings (losses) of unconsolidated affiliates	28.0	49.2	137.6	133.8
Equity in earnings (losses) of unconsolidated affiliates, net of tax	86.6	(11.9)	66.2	(37.9)
Net earnings	114.6	37.3	203.8	95.9
Net losses attributable to redeemable noncontrolling interests	13.2	0.0	13.2	0.0
Net earnings attributable to Black Knight	127.8	37.3	217.0	95.9
Share-based compensation expense	9.2	14.4	29.4	39.8
Operating Segments | Software Solutions
Segment Reporting Information [Line Items]
Revenues	259.5	257.3	749.3	756.2
Expenses:
Operating expenses	107.9	104.1	312.1	308.4
Transition and integration costs		0.0	0.0	0.0
EBITDA	151.6	153.2	437.2	447.8
Depreciation and amortization	30.6	31.4	91.1	91.4
Operating income (loss)	121.0	121.8	346.1	356.4
Operating Segments | Data and Analytics
Segment Reporting Information [Line Items]
Revenues	53.1	41.9	147.4	121.3
Expenses:
Operating expenses	34.8	31.4	98.4	91.5
Transition and integration costs		0.0	0.0	0.0
EBITDA	18.3	10.5	49.0	29.8
Depreciation and amortization	3.6	3.9	11.4	11.6
Operating income (loss)	14.7	6.6	37.6	18.2
Corporate and Other
Segment Reporting Information [Line Items]
Revenues	0.0	(0.1)	(0.3)	(0.4)
Expenses:
Operating expenses	24.5	28.4	74.6	83.4
Transition and integration costs	21.9	0.4	26.8	2.3
EBITDA	(46.4)	(28.9)	(101.7)	(86.1)
Depreciation and amortization	29.8	24.3	77.8	71.0
Operating income (loss)	(76.2)	(53.2)	(179.5)	(157.1)
Share-based compensation expense	$ 9.3	$ 14.5	$ 30.5	$ 40.6