Related Party Transactions (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 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	$ 186,000,000.0		$ 186,000,000.0		$ 181,900,000
Equity in earnings of unconsolidated affiliate	3,400,000	$ 6,000,000.0	4,600,000	$ 10,100,000
Related Party Transactions [Abstract]
Product manufactured for ART	60,200,000	59,300,000	131,300,000	126,100,000
Mark-up on product manufactured for ART included as a reduction of Grace’s cost of goods sold	1,200,000	1,200,000	2,600,000	2,500,000
Charges for fixed costs; research and development; selling, general and administrative services; and depreciation to ART	13,300,000	12,800,000	27,400,000	25,600,000
Investment in unconsolidated affiliates
Assets, Current	1,719,600,000		1,719,600,000		1,134,900,000
Total Assets	4,505,000,000.0		4,505,000,000.0		3,932,600,000
Liabilities, Current	1,360,600,000		1,360,600,000		745,100,000
Total Liabilities	4,155,400,000		4,155,400,000		3,530,400,000
Revenues	418,700,000	513,600,000	840,200,000	983,100,000
Cost of goods sold	299,400,000	304,200,000	561,300,000	585,100,000
Income (loss) before income taxes	(3,200,000)	95,200,000	54,600,000	130,700,000
Net Income (Loss) Attributable to Parent	(7,300,000)	76,200,000	34,700,000	100,900,000
Operating Income Included in Income (Loss) from Equity Method Investments	4,000,000.0	6,700,000	5,600,000	11,200,000
Depreciation and Amortization Included in Income (Loss) From Equity Method Investments	(400,000)	(100,000)	(800,000)	(200,000)
Interest Expense and Income Taxes Included in Income (Loss) From Equity Method Investments	(200,000)	(600,000)	$ (200,000)	(900,000)
Debt Instrument, Frequency of Periodic Payment			monthly
Loan Repayment Period, Max			P8Y
Current asset, related party	191,300,000		$ 191,300,000		173,900,000
Current liability, related party	191,300,000		191,300,000		173,900,000
Affiliated Entity [Member]
Investment in unconsolidated affiliates
Accounts receivable	2,100,000		2,100,000		3,600,000
Revenue from Related Parties	4,000,000.0	700,000	$ 5,900,000	3,900,000
ART [Member]
Investment in unconsolidated affiliates
Basis spread on variable rate			1.25%
Accounts receivable	15,200,000		$ 15,200,000		17,500,000
Current asset, related party	191,300,000		191,300,000		173,900,000
Accounts payable	25,300,000		25,300,000		37,700,000
Debt payable within one year	9,600,000		9,600,000		9,900,000
Debt payable after one year	37,800,000		37,800,000		37,500,000
Current liability, related party	191,300,000		191,300,000		173,900,000
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%
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	$ 285,300,000		$ 285,300,000		300,700,000
Assets, Noncurrent	256,400,000		256,400,000		237,800,000
Total Assets	541,700,000		541,700,000		538,500,000
Liabilities, Current	211,500,000		211,500,000		177,100,000
Liabilities, Noncurrent	300,000		300,000		300,000
Total Liabilities	211,800,000		211,800,000		$ 177,400,000
Revenues	124,400,000	120,000,000.0	199,700,000	231,500,000
Cost of goods sold	113,100,000	102,200,000	181,100,000	199,500,000
Income (loss) before income taxes	7,400,000	12,800,000	10,300,000	22,500,000
Net Income (Loss) Attributable to Parent	$ 6,600,000	$ 12,000,000.0	$ 9,100,000	$ 21,200,000