Earnings Per Share (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Feb. 08, 2017	Feb. 05, 2015
Numerators
Net income (loss) attributable to W. R. Grace & Co. Shareholders	$ 16,100,000	$ 47,400,000	$ 98,500,000	$ 134,200,000
Denominators
Weighted average number of basic shares (in shares)	67,100,000	67,900,000	67,300,000	68,200,000
Dilutive effect of employee stock options (in shares)	100,000	100,000	100,000	100,000
Weighted average common shares—diluted calculation (in shares)	67,200,000	68,000,000	67,400,000	68,300,000
Basic earnings per share attributable to W. R. Grace & Co. shareholders
Net income (loss) (in dollars per share)	$ 0.24	$ 0.70	$ 1.46	$ 1.97
Diluted earnings per share attributable to W. R. Grace & Co. shareholders
Net income (loss) (in dollars per shares)	$ 0.24	$ 0.70	$ 1.46	$ 1.96
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options outstanding (in shares)	1,400,000	1,600,000	1,400,000	1,500,000
Stock repurchase program, authorized amount					$ 250,000,000	$ 500,000,000
Stock repurchased during period (in shares)			865,698	935,435
Cash paid for repurchases of common stock			$ 60,100,000	$ 65,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 158,700,000		$ 158,700,000
Minimum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock repurchase program, period in force			12 months
Maximum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock repurchase program, period in force			24 months