Related Party Transactions (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Equity method investment ownership interest (percent)	50.00%		50.00%
Investment in unconsolidated affiliate	$ 167,400,000		$ 167,400,000		$ 181,900,000
Equity in earnings of unconsolidated affiliate	1,300,000	$ 3,800,000	5,900,000	$ 13,900,000
Related Party Transactions [Abstract]
Product manufactured for ART	63,400,000	64,100,000	194,700,000	190,200,000
Mark-up on product manufactured for ART included as a reduction of Grace’s cost of goods sold	1,200,000	1,200,000	3,800,000	3,700,000
Charges for fixed costs; research and development; selling, general and administrative services; and depreciation to ART	13,100,000	12,400,000	40,500,000	38,000,000.0
Investment in unconsolidated affiliates
Assets, Current	833,600,000		833,600,000		1,134,900,000
Total Assets	3,650,400,000		3,650,400,000		3,932,600,000
Liabilities, Current	495,200,000		495,200,000		745,100,000
Total Liabilities	3,329,900,000		3,329,900,000		3,530,400,000
Revenues	419,400,000	470,500,000	1,259,600,000	1,453,600,000
Cost of goods sold	263,000,000.0	279,500,000	824,300,000	864,600,000
Income (loss) before income taxes	(23,500,000)	81,100,000	31,100,000	211,800,000
Net Income (Loss) Attributable to Parent	7,000,000.0	53,700,000	41,700,000	154,600,000
Operating Income Included in Income (Loss) from Equity Method Investments	2,800,000	4,400,000	8,400,000	15,600,000
Depreciation and Amortization Included in Income (Loss) From Equity Method Investments	(1,100,000)	(200,000)	(1,900,000)	(400,000)
Interest Expense and Income Taxes Included in Income (Loss) From Equity Method Investments	(400,000)	(400,000)	$ (600,000)	(1,300,000)
Debt Instrument, Frequency of Periodic Payment			monthly
Loan Repayment Period, Max			P8Y
Current asset, related party	0		$ 0		173,900,000
Current liability, related party	0		0		173,900,000
Dividends received from unconsolidated affiliate	10,000,000.0		10,000,000.0	0
Affiliated Entity [Member]
Investment in unconsolidated affiliates
Accounts receivable	900,000		900,000		3,600,000
Revenue from Related Parties	700,000	1,800,000	$ 6,600,000	5,800,000
ART [Member]
Investment in unconsolidated affiliates
Basis spread on variable rate			1.25%
Accounts receivable	23,900,000		$ 23,900,000		17,500,000
Current asset, related party	10,000,000.0		10,000,000.0		173,900,000
Accounts payable	23,500,000		23,500,000		37,700,000
Debt payable within one year	4,800,000		4,800,000		9,900,000
Debt payable after one year	30,700,000		30,700,000		37,500,000
Current liability, related party	0		0		173,900,000
Dividends Receivable	10,000,000.0		10,000,000.0
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%
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
Joint Venture [Member]
Investment in unconsolidated affiliates
Noncontrolling Interest, Ownership Percentage by Parent	87.50%		87.50%
ART [Member]
Investment in unconsolidated affiliates
Assets, Current	$ 270,400,000		$ 270,400,000		300,700,000
Assets, Noncurrent	248,300,000		248,300,000		237,800,000
Total Assets	518,700,000		518,700,000		538,500,000
Liabilities, Current	185,800,000		185,800,000		177,100,000
Liabilities, Noncurrent	300,000		300,000		300,000
Total Liabilities	186,100,000		186,100,000		$ 177,400,000
Revenues	109,900,000	125,700,000	309,600,000	357,200,000
Cost of goods sold	100,000,000.0	113,300,000	281,100,000	312,800,000
Income (loss) before income taxes	3,100,000	8,100,000	13,400,000	30,600,000
Net Income (Loss) Attributable to Parent	$ 2,800,000	$ 7,600,000	$ 11,900,000	$ 28,800,000