Operating Segment Information - Reportable Segment Data (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) segment	Mar. 31, 2017 USD ($)
Operating segment information
Number of Reportable Segments | segment	2
Net Sales
Net sales	$ 431.5	$ 398.0
Adjusted EBIT
Total	95.8	86.8
Reconciliation of operating segment data to financial statements
(Costs) benefit related to legacy product, environmental and other claims	1.5	2.1
Restructuring and repositioning expenses	5.6	2.3
Pension MTM adjustment and other related costs, net	0.0	1.9
Income and expense items related to divested businesses	0.5	0.3
Third-party acquisition-related costs	0.9	0.0
Interest expense, net	(18.9)	(19.3)
Net income (loss) attributable to noncontrolling interests	0.2	0.0
Income (loss) before income taxes	$ 68.2	60.9
Grace Catalysts Technologies [Member]
Operating segment information
Number of Reportable Segments | segment	1
Number of operating segments | segment	2
Net Sales
Net sales	$ 315.8	293.8
Adjusted EBIT
Operating income	92.1	81.2
Grace Materials Technologies [Member]
Net Sales
Net sales	115.7	104.2	[1]
Adjusted EBIT
Operating income	24.1	24.8
Corporate, Non-Segment [Member]
Adjusted EBIT
Operating income	(16.6)	(16.1)
Certain pension costs	$ (3.8)	$ (3.1)

[1] (1)Under the modified retrospective method, prior-period information has not been adjusted and continues to be reported in accordance with Grace’s historical accounting under ASC 605.