Capital expenditures to fixed charges.

No definition available.

Name:	bgc_CapitalExpendituresToFixedChargesRatio
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Equity Interest Pledged

+ References

No definition available.

+ Details

Name:	bgc_EquityInterestPledged
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Equity Interest Pledged in All Domestic Subsidiaries, Percentage

+ References

No definition available.

+ Details

Name:	bgc_EquityInterestPledgedInAllDomesticSubsidiariesPercentage
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Non-Voting Equity Interest Pledged in Certain Foreign Subsidiaries, Percentage

+ References

No definition available.

+ Details

Name:	bgc_NonVotingEquityInterestPledgedInCertainForeignSubsidiariesPercentage
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Threshold For Line Of Credit Borrowing Capacity

+ References

No definition available.

+ Details

Name:	bgc_ThresholdForLineOfCreditBorrowingCapacity
Namespace Prefix:	bgc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Threshold for line of credit facility percentage of asset based revolving credit facililties

+ References

No definition available.

+ Details

Name:	bgc_ThresholdForLineOfCreditFacilityPercentageOfAssetBasedRevolvingCreditFacililties
Namespace Prefix:	bgc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityExpirationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Date the credit facility first became available, in CCYY-MM-DD format.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInitiationDate1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3255-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_ProceedsFromLinesOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_EuropeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_US
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_CA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Debt (Schedule Of Revolving Credit Facility) (Details) - USD ($)		3 Months Ended	12 Months Ended
	Sep. 06, 2013	Mar. 31, 2017	Dec. 31, 2016	Nov. 15, 2016	Feb. 09, 2016	Dec. 31, 2012	Jul. 22, 2011
Debt Instrument [Line Items]
Outstanding borrowings		$ 1,052,500,000	$ 938,600,000
Outstanding letters of credit		23,800,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity				$ 700,000,000	$ 1,000,000,000.0	$ 700,000,000	$ 400,000,000
Increase, additional borrowings	$ 250,000,000
Capital expenditures to fixed charges ratio	100.00%
Threshold for line of credit facility percentage of asset based revolving credit facilities	10.00%
Equity interest pledged in all domestic subsidiaries, percentage	100.00%
Equity interest pledged	65.00%
Non-voting equity interest pledged in certain foreign subsidiaries, percentage	100.00%
Outstanding borrowings		215,000,000	75,900,000
Total credit under facility		700,000,000	700,000,000
Undrawn availability		$ 316,700,000	$ 399,000,000
Interest rate		2.90%	2.50%
Outstanding letters of credit		$ 20,700,000	$ 21,700,000
Original issuance		Jul. 31, 2011	Jul. 31, 2011
Maturity date		Sep. 30, 2018	Sep. 30, 2018
Revolving Credit Facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Threshold for line of credit facility borrowings	$ 100,000,000
Commitment fee percentage	0.25%
Undrawn availability		$ 100,000,000
Revolving Credit Facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Commitment fee percentage	0.375%
Revolving Credit Facility [Member] \| Europe [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity				210,000,000
Outstanding borrowings		21,300,000	$ 0
Undrawn availability		67,900,000	97,400,000
Revolving Credit Facility [Member] \| United States [Member]
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity				441,000,000
Undrawn availability		200,300,000	265,000,000
Revolving Credit Facility [Member] \| CANADA
Debt Instrument [Line Items]
Credit facility maximum borrowing capacity				$ 49,000,000
Undrawn availability		$ 48,500,000	$ 36,600,000