Related Party Transactions (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	$ 165,700,000		$ 165,700,000		$ 156,100,000
Equity in earnings of unconsolidated affiliate	(6,000,000.0)	$ (8,200,000)	(10,100,000)	$ (13,600,000)
ART's assets, liabilities and results of operations
Current assets	281,300,000		281,300,000		307,400,000
Noncurrent assets	204,300,000		204,300,000		160,200,000
Total assets	485,600,000		485,600,000		467,600,000
Current liabilities	156,900,000		156,900,000		158,300,000
Noncurrent liabilities	300,000		300,000		300,000
Total liabilities	157,200,000		157,200,000		158,600,000
Net sales	120,000,000.0	103,000,000.0	231,500,000	188,200,000
Costs and expenses applicable to net sales	102,200,000	84,000,000.0	199,500,000	154,700,000
Income before income taxes	12,800,000	16,900,000	22,500,000	28,200,000
Net income	12,000,000.0	16,200,000	21,200,000	27,700,000
Related Party Transactions [Abstract]
Product manufactured for ART	59,300,000	58,500,000	126,100,000	110,400,000
Mark-up on product manufactured for ART included as a reduction of Grace’s cost of goods sold	1,200,000	1,200,000	2,500,000	2,200,000
Charges for fixed costs; research and development; selling, general and administrative services; and depreciation to ART	12,800,000	10,400,000	$ 25,600,000	21,100,000
Investment in unconsolidated affiliates
Debt Instrument, Frequency of Periodic Payment			monthly
Loan Repayment Period, Max			P8Y
Document Period End Date			Jun. 30, 2019
Current asset, related party	143,800,000		$ 143,800,000		0
Current liability, related party	143,800,000		143,800,000		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	13,500,000		$ 13,500,000		16,200,000
Current asset	0		0		98,800,000
Current asset, related party	143,800,000		143,800,000		0
Accounts payable	28,600,000		28,600,000		32,000,000.0
Debt payable within one year	9,500,000		9,500,000		9,800,000
Debt payable after one year	37,900,000		37,900,000		38,300,000
Current liability, related party	143,800,000		143,800,000		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	700,000		$ 700,000		3,700,000
Revenue from Related Parties	$ 700,000	$ 3,800,000	$ 3,900,000	$ 3,800,000
Noncontrolling Interest, Ownership Percentage by Parent	87.50%		87.50%
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