Condensed Consolidated Statements of Earnings and Comprehensive Earnings - USD ($) shares in Millions, $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2020		Sep. 30, 2019		Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenues		$ 312.6		$ 299.1		$ 896.4	$ 877.1
Expenses:
Operating expenses		167.2		163.9		485.1	483.3
Depreciation and amortization		64.0		59.6		180.3	174.0
Transition and integration costs		21.9		0.4		26.8	2.3
Total expenses		253.1		223.9		692.2	659.6
Operating income (loss)		59.5		75.2		204.2	217.5
Other income and expense:
Interest expense		(14.7)		(16.5)		(42.4)	(48.2)
Other (expense) income, net		(0.9)		(0.1)		17.1	(0.9)
Total other expense, net		(15.6)		(16.6)		(25.3)	(49.1)
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 Income (Loss) Attributable to Parent, Total		127.8		37.3		217.0	95.9
Unrealized holding gains (losses), net of tax(1)	[1]	0.1		(3.0)		(24.1)	(21.0)
Reclassification adjustments for losses (gains) included in net earnings, net of tax(2)	[2]	(3.9)		(0.1)		(8.3)	0.9
Reclassification adjustments for losses (gains) included in net earnings, net of tax(2)		4.0		(2.9)		(15.8)	(21.9)
Foreign currency translation adjustment	[3]	0.1		0.0		(0.1)	0.0
Unrealized loss on investments in unconsolidated affiliates	[4]	4.7		(3.4)		3.0	(5.8)
Other comprehensive earnings (losses)		8.8		(6.3)		(12.9)	(27.7)
Comprehensive earnings		123.4		31.0		190.9	68.2
Comprehensive earnings attributable to Black Knight		$ 136.6		$ 31.0		$ 204.1	$ 68.2
Net earnings per share attributable to Black Knight shareholders:
Basic (in dollars per share)		$ 0.82		$ 0.25		$ 1.44	$ 0.65
Diluted (in dollars per share)		$ 0.82		$ 0.25		$ 1.43	$ 0.65
Weighted average shares of common stock outstanding (Note 4):
Basic (in shares)		155.4	[4]	147.7	[4]	150.9	147.6
Diluted (in shares)		156.3	[4]	148.5	[4]	151.7	148.4
Derivatives qualifying as hedges, tax		$ 0.1		$ 1.0		$ 8.2	$ 7.4
Reclassification adjustment from AOCI on derivatives, tax		(1.3)		(0.1)		(2.8)	0.3
Foreign currency translation adjustment, tax benefit						0.1
Unrealized loss on investments in unconsolidated affiliates, tax benefit		$ 1.6		$ (1.1)		$ 1.0	$ (2.0)

[1] Net of income tax expense of less than $0.1 million and income tax benefit of $8.2 million for the three and nine months ended September 30, 2020, respectively, and income tax benefit of $1.0 million and $7.4 million for the three and nine months ended September 30, 2019, respectively.

[2] Amounts reclassified to net earnings relate to losses (gains) on interest rate swaps and are included in Interest expense, net above. Amounts are net of income tax benefit of $1.3 million and $2.8 million for the three and nine months ended September 30, 2020, respectively, and income tax benefit of less than $0.1 million and income tax expense of $0.3 million for the three and nine months ended September 30, 2019, respectively.

[3] Net of income tax expense of less than $0.1 million and income tax benefit of less than $0.1 million for the three and nine months ended September 30, 2020, respectively.

[4] 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.