Consolidated Statements of Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales	$ 494.9	$ 429.5	$ 1,412.1	$ 1,257.0
Cost of goods sold	292.7	258.2	841.7	765.3
Gross profit	202.2	171.3	570.4	491.7
Selling, general and administrative expenses	75.6	69.3	227.1	204.1
Research and development expenses	15.7	14.0	46.5	41.5
Provision for environmental remediation, net	72.7	6.4	73.3	19.6
Equity in earnings of unconsolidated affiliate	(5.9)	(4.8)	(19.5)	(17.9)
Restructuring and repositioning expenses	8.4	9.3	32.8	17.0
Interest expense and related financing costs	20.4	20.1	59.6	59.7
Other (income) expense, net	(1.3)	(1.7)	2.2	(15.0)
Total costs and expenses	185.6	112.6	422.0	309.0
Income (loss) before income taxes	16.6	58.7	148.4	182.7
(Provision for) benefit from income taxes	(0.7)	(11.6)	(50.5)	(49.2)
Net income (loss)	15.9	47.1	97.9	133.5
Less: Net (income) loss attributable to noncontrolling interests	0.2	0.3	0.6	0.7
Net income (loss) attributable to W. R. Grace & Co. shareholders	$ 16.1	$ 47.4	$ 98.5	$ 134.2
Basic earnings per share:
Net income (loss) (in dollars per share)	$ 0.24	$ 0.70	$ 1.46	$ 1.97
Weighted average number of basic shares (in shares)	67.1	67.9	67.3	68.2
Diluted earnings per share:
Net income (loss) (in dollars per shares)	$ 0.24	$ 0.70	$ 1.46	$ 1.96
Weighted average number of diluted shares (in shares)	67.2	68.0	67.4	68.3
Dividends per common share (in dollars per shares)	$ 0.24	$ 0.21	$ 0.72	$ 0.63