Earnings Per Share (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Feb. 08, 2017
Numerators
Net income (loss) attributable to W. R. Grace & Co. Shareholders	$ 24,700,000	$ 43,600,000
Denominators
Weighted average number of basic shares (in shares)	66,800,000	67,600,000
Dilutive effect of employee stock options (in shares)	100,000	100,000
Weighted average common shares—diluted calculation (in shares)	66,900,000	67,700,000
Basic earnings per share attributable to W. R. Grace & Co. shareholders
Net income (loss) (in dollars per share)	$ 0.37	$ 0.64
Diluted earnings per share attributable to W. R. Grace & Co. shareholders
Net income (loss) (in dollars per shares)	$ 0.37	$ 0.64
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options outstanding (in shares)	900,000	1,700,000
Stock repurchase program, authorized amount			$ 250,000,000
Stock repurchased during period (in shares)	69,860	514,141
Cash paid for repurchases of common stock	$ 4,800,000	$ 35,000,000.0
Stock repurchase program, remaining authorized repurchase amount	$ 134,100,000