Consolidated Statements of Operations (unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
Revenues	$ 513.6	$ 485.7	$ 983.1	$ 917.2
Cost of goods sold	304.2	287.0	585.1	549.0
Gross profit	209.4	198.7	398.0	368.2
Selling, general and administrative expenses	76.3	80.4	149.5	148.8
Research and development expenses	16.3	16.1	33.3	30.8
Costs related to legacy matters	1.5	2.2	48.4	4.2
Equity in earnings of unconsolidated affiliate	(6.0)	(8.2)	(10.1)	(13.6)
Restructuring and repositioning expenses	6.4	18.8	8.7	24.4
Interest expense and related financing costs	19.6	19.9	39.6	39.2
Other (income) expense, net	0.1	5.9	(2.1)	2.6
Total costs and expenses	114.2	135.1	267.3	236.4
Income (loss) before income taxes	95.2	63.6	130.7	131.8
(Provision for) benefit from income taxes	(18.8)	(25.0)	(29.7)	(49.8)
Net income (loss)	76.4	38.6	101.0	82.0
Less: Net (income) loss attributable to noncontrolling interests	(0.2)	0.2	(0.1)	0.4
Net income (loss) attributable to W. R. Grace & Co. shareholders	$ 76.2	$ 38.8	$ 100.9	$ 82.4
Basic earnings per share:
Net income (loss) (in dollars per share)	$ 1.14	$ 0.58	$ 1.51	$ 1.22
Weighted average number of basic shares (in shares)	66.8	67.3	66.8	67.4
Diluted earnings per share:
Net income (loss) (in dollars per shares)	$ 1.14	$ 0.58	$ 1.51	$ 1.22
Weighted average number of diluted shares (in shares)	67.0	67.4	66.9	67.5
Dividends per common share (in dollars per shares)	$ 0.27	$ 0.24	$ 0.54	$ 0.48