Consolidated Statements of Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement [Abstract]
Net sales	$ 429.5	$ 404.5	$ 1,257.0	$ 1,157.8
Cost of goods sold	256.2	236.3	761.2	663.7
Gross profit	173.3	168.2	495.8	494.1
Selling, general and administrative expenses	70.5	67.1	207.3	201.5
Research and development expenses	13.3	12.1	39.4	36.2
Provision for environmental remediation, net	6.4	11.9	19.6	19.4
Equity in earnings of unconsolidated affiliate	(4.8)	(8.5)	(17.9)	(18.0)
Restructuring and repositioning expenses	9.3	5.6	17.0	28.6
Interest expense and related financing costs	20.1	19.8	59.7	61.6
Other (income) expense, net	(0.2)	(0.5)	(12.0)	13.3
Total costs and expenses	114.6	107.5	313.1	342.6
Income (loss) from continuing operations before income taxes	58.7	60.7	182.7	151.5
(Provision for) benefit from income taxes	(11.6)	(19.4)	(49.2)	(62.1)
Income (loss) from continuing operations	47.1	41.3	133.5	89.4
Income (loss) from discontinued operations, net of income taxes	0.0	(1.6)	0.0	(10.9)
Net income (loss)	47.1	39.7	133.5	78.5
Less: Net (income) loss attributable to noncontrolling interests	0.3	(0.1)	0.7	0.3
Net income (loss) attributable to W. R. Grace & Co. shareholders	47.4	39.6	134.2	78.8
Amounts Attributable to W. R. Grace & Co. Shareholders:
Income (loss) from continuing operations attributable to W. R. Grace & Co. shareholders	$ 47.4	$ 41.2	$ 134.2	$ 89.7
Basic earnings per share:
Income (loss) from continuing operations	$ 0.70	$ 0.59	$ 1.97	$ 1.27
Income (loss) from discontinued operations, net of income taxes	0.00	(0.03)	0.00	(0.15)
Net income (loss)	$ 0.70	$ 0.56	$ 1.97	$ 1.12
Weighted average number of basic shares	67.9	70.3	68.2	70.5
Diluted earnings per share:
Income (loss) from continuing operations	$ 0.70	$ 0.58	$ 1.96	$ 1.27
Income (loss) from discontinued operations, net of income taxes	0.00	(0.02)	0.00	(0.16)
Net income (loss)	$ 0.70	$ 0.56	$ 1.96	$ 1.11
Weighted average number of diluted shares	68.0	70.7	68.3	70.9
Dividends per common share	$ 0.21	$ 0.17	$ 0.63	$ 0.34