Unconsolidated Affiliate (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
Equity method investment ownership interest (percent)	50.00%		50.00%
Investment in unconsolidated affiliate	$ 138,700,000		$ 138,700,000		$ 125,900,000
Equity in earnings of unconsolidated affiliate	(8,200,000)	$ (6,100,000)	(13,600,000)	$ (13,100,000)
ART's assets, liabilities and results of operations
Current assets	293,000,000		293,000,000		239,800,000
Noncurrent assets	119,600,000		119,600,000		91,500,000
Total assets	412,600,000		412,600,000		331,300,000
Current liabilities	138,600,000		138,600,000		82,400,000
Noncurrent liabilities	300,000		300,000		300,000
Total liabilities	138,900,000		138,900,000		82,700,000
Net sales	103,000,000	110,500,000	188,200,000	207,900,000
Costs and expenses applicable to net sales	84,000,000	94,700,000	154,700,000	173,600,000
Income before income taxes	16,900,000	12,600,000	28,200,000	26,800,000
Net income	16,200,000	12,200,000	27,700,000	26,200,000
Related Party Transactions [Abstract]
Product manufactured for ART	58,500,000	53,100,000	110,400,000	104,500,000
Mark-up on product manufactured for ART included as a reduction of Grace’s cost of goods sold	1,200,000	1,000,000	2,200,000	2,000,000
Charges for fixed costs; research and development; selling, general and administrative services; and depreciation to ART	10,400,000	$ 10,400,000	21,100,000	$ 20,800,000
Investment in unconsolidated affiliates
Accounts receivable	15,500,000		15,500,000		20,100,000
Noncurrent asset	56,000,000		56,000,000		32,700,000
Accounts payable	32,600,000		32,600,000		22,300,000
Debt payable within one year	8,700,000		8,700,000		8,600,000
Debt payable after one year	37,600,000		37,600,000		33,800,000
Liability to unconsolidated affiliate	56,000,000		56,000,000		32,700,000
Grace
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
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%