Fair Value Measurements and Risk - Carrying Amounts and Fair Values of Debt (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	$ 1,986.6	$ 1,543.9
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other borrowings	54.5	55.1
Total debt	1,986.6	1,543.9
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other borrowings	54.5	55.1
Total debt	2,014.1	1,608.5
Term Loan B (USD)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unamortized discount and debt issuance costs		4.3
Term Loan B (USD) \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	0.0	404.1
Term Loan B (USD) \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	0.0	409.7
Term Loan B (EUR)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unamortized discount and debt issuance costs		1.0
Term Loan B (EUR) \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	0.0	94.0
Term Loan B (EUR) \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	0.0	93.7
2025 Term Loan
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	940.3	0.0
Unamortized discount and debt issuance costs	9.7	0.0
2025 Term Loan \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	940.3	0.0
2025 Term Loan \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	939.1	0.0
5.125% Senior Notes, Due 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	$ 695.0	$ 694.2
Interest rate (percent)	5.125%	5.125%
Unamortized discount and debt issuance costs	$ 5.0	$ 5.8
5.125% Senior Notes, Due 2021 \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	695.0	694.2
5.125% Senior Notes, Due 2021 \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	709.2	728.7
5.625% Senior Notes, Due 2024
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	$ 296.8	$ 296.5
Interest rate (percent)	5.625%	5.625%
Unamortized discount and debt issuance costs	$ 3.2	$ 3.5
5.625% Senior Notes, Due 2024 \| Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	296.8	296.5
5.625% Senior Notes, Due 2024 \| Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total debt	$ 311.3	$ 321.3

Contractual interest rate for funds borrowed, under the debt agreement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of unamortized debt discount (premium) and debt issuance costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

+ Details

Name:	us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the aggregate of total long-term debt, including current maturities and short-term debt.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtLongtermAndShorttermCombinedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13,16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_OtherBorrowings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_EstimateOfFairValueFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=gra_TermLoanBUSDMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=gra_TermLoanBEURMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gra_A2025TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gra_SeniorNotesDue2021Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gra_SeniorNotesDue2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: