Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerators
Net income attributable to W. R. Grace and Co. shareholders	$ 75.5	$ 81.3	$ 205.7	$ 211.3
Denominators
Weighted average common shares-basic calculation	75.0	73.7	74.7	73.5
Dilutive effect of employee stock options (in shares)	1.4	2.0	1.5	2.0
Weighted average common shares-diluted calculation	76.4	75.7	76.2	75.5
Basic earnings per share	$ 1.01	$ 1.10	$ 2.75	$ 2.87
Diluted earnings per share	$ 0.99	$ 1.07	$ 2.70	$ 2.80
Stock options excluded from computation of diluted earnings per share	0.8	1.3	0.3	1.3
Number of warrants not included in diluted earnings per share	10		10

Number of warrants authorized by entity to fund trust.

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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