Document and Entity Information - shares
6 Months Ended
Jun. 30, 2018
Jul. 31, 2018
Document and Entity Information    
Entity Registrant Name W R GRACE & CO  
Entity Central Index Key 0001045309  
Document Type 10-Q  
Document Period End Date Jun. 30, 2018  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Common Stock, Shares Outstanding   67,238,067
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2