Earnings Per Share (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Feb. 28, 2020	Feb. 08, 2017
Numerators
Net Income (Loss) Attributable to Parent	$ 42,000,000.0	$ 24,700,000
Denominators
Weighted average number of basic shares (in shares)	66,500,000	66,800,000
Dilutive effect of employee stock options (in shares)	0	100,000
Weighted average common shares—diluted calculation (in shares)	66,500,000	66,900,000
Basic earnings per share attributable to W. R. Grace & Co. shareholders
Net income (loss) (in dollars per share)	$ 0.63	$ 0.37
Diluted earnings per share attributable to W. R. Grace & Co. shareholders
Net income (loss) (in dollars per shares)	$ 0.63	$ 0.37
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive options outstanding (in shares)	1,700,000	900,000
Stock repurchase program, authorized amount			$ 250,000,000	$ 250,000,000
Stock repurchased during period (in shares)	673,807	69,860
Cash paid for repurchases of common stock	$ 40,400,000	$ 4,800,000
Stock repurchase program, remaining authorized repurchase amount	$ 235,000,000.0
2/8/2017 Share Repurchase Program [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Stock repurchase program, remaining authorized repurchase amount			$ 83,000,000