Related Party Transactions (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity method investment ownership interest (percent)	50.00%
Investment in unconsolidated affiliate	$ 159,500,000		$ 156,100,000
Equity in earnings of unconsolidated affiliate	(4,100,000)	$ (5,400,000)
ART's assets, liabilities and results of operations
Current assets	307,800,000		307,400,000
Noncurrent assets	177,000,000.0		160,200,000
Total assets	484,800,000		467,600,000
Current liabilities	168,500,000		158,300,000
Noncurrent liabilities	300,000		300,000
Total liabilities	168,800,000		158,600,000
Net sales	111,500,000	85,200,000
Costs and expenses applicable to net sales	97,300,000	70,700,000
Income before income taxes	9,700,000	11,300,000
Net income	9,200,000	11,500,000
Related Party Transactions [Abstract]
Product manufactured for ART	66,800,000	51,900,000
Mark-up on product manufactured for ART included as a reduction of Grace’s cost of goods sold	1,300,000	1,000,000.0
Charges for fixed costs; research and development; selling, general and administrative services; and depreciation to ART	$ 12,800,000	$ 10,700,000
Investment in unconsolidated affiliates
Debt Instrument, Frequency of Periodic Payment	monthly
Loan Repayment Period, Max	8 years
Document Period End Date	Mar. 31, 2019
Current asset, related party	$ 114,500,000		0
Current liability, related party	114,500,000		0
Liability to unconsolidated affiliate (see Note 15)	$ 0		98,800,000
ART [Member]
Investment in unconsolidated affiliates
Basis spread on variable rate	1.25%
Accounts receivable	$ 12,900,000		16,200,000
Noncurrent asset	0		98,800,000
Current asset, related party	114,500,000		0
Accounts payable	27,700,000		32,000,000.0
Debt payable within one year	9,800,000		9,800,000
Debt payable after one year	37,900,000		38,300,000
Current liability, related party	114,500,000		0
Liability to unconsolidated affiliate (see Note 15)	0		98,800,000
Grace LOC to ART [Member]
Investment in unconsolidated affiliates
Line of credit facility, maximum provided by Grace and Chevron each	$ 15,000,000.0
Commitment fee on credit facility (as a percent)	0.10%
Joint Venture [Member]
Investment in unconsolidated affiliates
Accounts receivable	$ 3,200,000		3,700,000
Revenue from Related Parties	$ 3,200,000
Noncontrolling Interest, Ownership Percentage by Parent	87.50%
Chevron
Investment in unconsolidated affiliates
Line of credit facility, maximum provided by Grace and Chevron each	$ 15,000,000.0
Commitment fee on credit facility (as a percent)	0.10%
Credit facility amount outstanding	$ 0		$ 0