Note 11 - Stockholders' Equity - Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Foreign currency translation adjustment attributable to Verisk, before tax		$ (30.7)	$ (233.0)	$ 44.0	$ (522.8)
Foreign currency translation adjustment attributable to Verisk, tax		0.0	0.0	0.0	0.0
Foreign currency translation adjustment attributable to Verisk, after tax		(30.7)	(233.0)	44.0	(522.8)
Foreign currency translation adjustment attributable to noncontrolling interests, before tax		(1.1)	(1.2)	(1.2)	(2.7)
Foreign currency translation adjustment attributable to noncontrolling interests, tax		0.0	0.0	0.0	0.0
Foreign currency translation adjustment attributable to noncontrolling interests, after tax		(1.1)	(1.2)	(1.2)	(2.7)
Foreign currency translation adjustment, before tax		(31.8)	(234.2)	743.4	(525.5)
Foreign currency translation adjustment, tax		0.0	0.0	0.0	0.0
Foreign currency translation adjustment, after tax		(31.8)	(234.2)	743.4	(525.5)
Total other comprehensive loss		(30.8)	(233.6)	746.5	(523.7)
Total other comprehensive loss		(0.2)	(0.3)	(0.7)	(0.5)
Total other comprehensive loss		(31.0)	(233.9)	745.8	(524.2)
Cumulative translation adjustment recognized upon deconsolidation of the Energy business, before tax				700.6
Cumulative translation adjustment recognized upon deconsolidation of the Energy business, tax				0.0
Cumulative translation adjustment recognized upon deconsolidation of the Energy business, after tax				700.6
Pension and Postretirement Adjustment [Member]
Other comprehensive income (loss), before reclassifications, before tax		2.3	1.5	7.2	4.2
Other comprehensive income (loss), before reclassifications, tax		(0.5)	(0.4)	(1.7)	(1.1)
Other comprehensive income (loss), before reclassifications, after tax		1.8	1.1	5.5	3.1
Amortization of net actuarial loss and prior service benefit reclassified from accumulated other comprehensive income (losses), before tax	[1]	(1.3)	(0.9)	(4.1)	(2.4)
Amortization of net actuarial loss and prior service benefit reclassified from accumulated other comprehensive income (loss), tax	[1]	0.3	0.1	1.0	0.6
Amortization of net actuarial loss and prior service benefit reclassified from accumulated other comprehensive income (losses), after tax	[1]	(1.0)	(0.8)	(3.1)	(1.8)
Other comprehensive income (loss), before tax		1.0	0.6	3.1	1.8
Other comprehensive income (loss), tax		(0.2)	(0.3)	(0.7)	(0.5)
Other comprehensive income (loss), after tax		$ 0.8	$ 0.3	$ 2.4	$ 1.3

[1] These accumulated other comprehensive loss components, before tax, are included under "Cost of revenues" and "Selling, general and administrative" in our accompanying consolidated statements of operations. These components are also included in the computation of net periodic (benefit) cost (See Note 18. Pension and Postretirement Benefits for additional details).