Segment information - Segment Sales (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information, Profit (Loss)
Net sales	$ 229.5	$ 264.1	$ 260.3	$ 218.5	$ 210.9	$ 252.4	$ 245.4	$ 199.6	$ 972.4	$ 908.3	$ 958.3
Segment operating profits									202.3	163.6	166.3
Separation costs									(0.9)	(17.5)	(17.2)
Restructuring and other income (charges)									(3.7)	(41.2)	7.5
Acquisition costs									(7.1)	0.0	0.0
Interest expense									(18.1)	(19.3)	(20.1)
Interest income									2.3	1.4	0.0
Provision for income taxes									(29.6)	(42.6)	(52.2)
Less: Net income (loss) attributable to noncontrolling interests, net of taxes	(6.4)	(4.6)	(3.7)	(4.0)	(2.6)	(2.3)	(1.8)	(2.5)	(18.7)	(9.2)	(4.6)
Net income (loss) attributable to Ingevity stockholders	$ 41.6	$ 33.8	$ 32.1	$ 19.0	$ 9.1	$ (7.2)	$ 24.1	$ 9.2	126.5	35.2	79.7
Performance Materials
Segment Reporting Information, Profit (Loss)
Net sales									349.3	301.0	256.4
Segment operating profits									122.0	106.9	79.7
Performance Chemicals
Segment Reporting Information, Profit (Loss)
Net sales									623.1	607.3	701.9
Segment operating profits									$ 80.3	$ 56.7	$ 86.6