Related Party Transactions (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
Equity method investment ownership interest (percent)	50.00%		50.00%
Investment in unconsolidated affiliate	$ 168,500,000		$ 168,500,000		$ 156,100,000
Equity in earnings of unconsolidated affiliate	(3,800,000)	$ (5,900,000)	(13,900,000)	$ (19,500,000)
ART's assets, liabilities and results of operations
Current assets	273,900,000		273,900,000		307,400,000
Noncurrent assets	220,700,000		220,700,000		160,200,000
Total assets	494,600,000		494,600,000		467,600,000
Current liabilities	160,300,000		160,300,000		158,300,000
Noncurrent liabilities	300,000		300,000		300,000
Total liabilities	160,600,000		160,600,000		158,600,000
Net sales	125,700,000	120,200,000	357,200,000	308,400,000
Costs and expenses applicable to net sales	113,300,000	105,000,000.0	312,800,000	259,700,000
Income before income taxes	8,100,000	12,500,000	30,600,000	40,700,000
Net income	7,600,000	11,800,000	28,800,000	39,500,000
Related Party Transactions [Abstract]
Product manufactured for ART	64,100,000	58,700,000	190,200,000	169,100,000
Mark-up on product manufactured for ART included as a reduction of Grace’s cost of goods sold	1,200,000	1,100,000	3,700,000	3,300,000
Charges for fixed costs; research and development; selling, general and administrative services; and depreciation to ART	12,400,000	10,500,000	$ 38,000,000.0	31,600,000
Investment in unconsolidated affiliates
Debt Instrument, Frequency of Periodic Payment			monthly
Loan Repayment Period, Max			P8Y
Current asset, related party	158,100,000		$ 158,100,000		0
Current liability, related party	158,100,000		158,100,000		0
Liability to unconsolidated affiliate (see Note 15)	0		$ 0		98,800,000
ART [Member]
Investment in unconsolidated affiliates
Basis spread on variable rate			1.25%
Accounts receivable	8,800,000		$ 8,800,000		16,200,000
Current asset, related party	158,100,000		158,100,000		0
Current asset	0		0		98,800,000
Accounts payable	29,600,000		29,600,000		32,000,000.0
Debt payable within one year	9,200,000		9,200,000		9,800,000
Debt payable after one year	39,000,000.0		39,000,000.0		38,300,000
Current liability, related party	158,100,000		158,100,000		0
Liability to unconsolidated affiliate (see Note 15)	0		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		$ 15,000,000.0
Commitment fee on credit facility (as a percent)			0.10%
Joint Venture [Member]
Investment in unconsolidated affiliates
Accounts receivable	$ 1,500,000		$ 1,500,000		3,700,000
Noncontrolling Interest, Ownership Percentage by Parent	87.50%		87.50%
Revenue from Related Parties	$ 1,800,000	$ 3,500,000	$ 5,800,000	$ 7,400,000
Chevron
Investment in unconsolidated affiliates
Line of credit facility, maximum provided by Grace and Chevron each	15,000,000.0		$ 15,000,000.0
Commitment fee on credit facility (as a percent)			0.10%
Credit facility amount outstanding	$ 0		$ 0		$ 0