Long-Term Debt (Subordinated Convertible Notes and Terms) (Details) (Subordinated Convertible Notes Due 2029 [Member], USD $)	12 Months Ended
Dec. 31, 2014
Debt Instrument [Line Items]
Debt instrument, beginning date	Aug. 31, 2029
Conversion price per share	$ 36.75
Conversion, shares per $1,000 principal amount of notes	27.2109
Principal amount of notes	$ 1,000
Common stock covered under note hedges	11,686,075bgc_CommonStockCoveredUnderNoteHedges
Make-Whole [Member]
Debt Instrument [Line Items]
Common stock covered under note hedges	14,315,419
Any Calendar Quarted after March 31, 2010 [Member]
Debt Instrument [Line Items]
Closing price as percent	130.00%
Consecutive trading days	30 days
Contingent, conversion price	$ 47.78
Any Calendar Quarted after March 31, 2010 [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Trading days	20 days
During Any Five Business Days [Member]
Debt Instrument [Line Items]
Closing price as percent	98.00%
During Any Five Business Days [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Trading days	5 days
On or After November 15, 2019 [Member]
Debt Instrument [Line Items]
Closing price as percent	150.00%
Consecutive trading days	30 days
On or After November 15, 2019 [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Trading days	20 days

Shares that could be issued due to the conversion of warrants.

No definition available.

Name:	bgc_CommonStockCoveredUnderNoteHedges
Namespace Prefix:	bgc_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Contingent, Conversion Price

+ References

No definition available.

+ Details

Name:	bgc_DebtInstrumentContingentConversionPrice
Namespace Prefix:	bgc_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Convertible, Conversion Shares per $1,000 Principal Amount of Notes

+ References

No definition available.

+ Details

Name:	bgc_DebtInstrumentConvertibleConversionSharesPer1000PrincipalAmountOfNotes
Namespace Prefix:	bgc_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument, Principal Amount of Notes

+ References

No definition available.

+ Details

Name:	bgc_DebtInstrumentPrincipalAmountOfNotes
Namespace Prefix:	bgc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Period, Consecutive Trading Days1

+ References

No definition available.

+ Details

Name:	bgc_PeriodConsecutiveTradingDays1
Namespace Prefix:	bgc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Period, trading days

+ References

No definition available.

+ Details

Name:	bgc_PeriodTradingDays
Namespace Prefix:	bgc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Premium over the closing price of the Companys shares of common stock included in strick price

+ References

No definition available.

+ Details

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

- Definition

Earliest date before maturity when the issuer can call the outstanding debt instrument for repayment or conversion to equity, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

+ Details

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

- Definition

The price per share of the conversion feature embedded in the debt instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6928298&loc=SL6031898-161870

+ Details

Name:	us-gaap_DebtInstrumentConvertibleConversionPrice1
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Details

Name:	bgc_TriggeringEventsAxis=bgc_AnyCalendarQuartedafterMarch312010Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bgc_TriggeringEventsAxis=bgc_DuringAnyFiveBusinessDaysMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	bgc_TriggeringEventsAxis=bgc_OnorAfterNovember152019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: