Consolidated Statements of Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net sales	$ 485.7	$ 429.5	$ 917.2	$ 827.5
Cost of goods sold	287.0	262.3	549.0	507.1
Gross profit	198.7	167.2	368.2	320.4
Selling, general and administrative expenses	82.2	69.3	151.5	134.8
Research and development expenses	16.1	13.6	30.8	27.5
Provision for environmental remediation, net	0.5	13.2	0.6	13.2
Equity in earnings of unconsolidated affiliate	(8.2)	(6.1)	(13.6)	(13.1)
Restructuring and repositioning expenses	18.8	5.4	24.4	7.7
Interest expense and related financing costs	19.9	20.1	39.2	39.6
Other (income) expense, net	5.8	(11.4)	3.5	(13.3)
Total costs and expenses	135.1	104.1	236.4	196.4
Income (loss) before income taxes	63.6	63.1	131.8	124.0
(Provision for) benefit from income taxes	(25.0)	(19.6)	(49.8)	(37.6)
Net income (loss)	38.6	43.5	82.0	86.4
Less: Net (income) loss attributable to noncontrolling interests	0.2	0.4	0.4	0.4
Net income (loss) attributable to W. R. Grace & Co. shareholders	$ 38.8	$ 43.9	$ 82.4	$ 86.8
Basic earnings per share:
Net income (loss) (in dollars per share)	$ 0.58	$ 0.64	$ 1.22	$ 1.27
Weighted average number of basic shares (in shares)	67.3	68.3	67.4	68.3
Diluted earnings per share:
Net income (loss) (in dollars per shares)	$ 0.58	$ 0.64	$ 1.22	$ 1.27
Weighted average number of diluted shares (in shares)	67.4	68.4	67.5	68.5
Dividends per common share (in dollars per shares)	$ 0.24	$ 0.21	$ 0.48	$ 0.42