Variable Interest Entities (Summary of Key Terms of NMTC Transactions) (Details) - Primary Beneficiary $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
NMTC 2
Variable Interest Entity [Line Items]
Loan Amount	$ 37.7
Interest Rate on Loan	1.00%
NMTC 2 \| Minimum
Variable Interest Entity [Line Items]
Interest Rate on Loan	0.71%
NMTC 2 \| Maximum
Variable Interest Entity [Line Items]
Interest Rate on Loan	0.77%
NMTC 2 \| US Bancorp
Variable Interest Entity [Line Items]
Financial Support to Other Entity	$ 17.5
NMTC 2 \| Unicom
Variable Interest Entity [Line Items]
Financial Support to Other Entity	52.0
NMTC 3
Variable Interest Entity [Line Items]
Loan Amount	$ 8.2
Interest Rate on Loan	1.00%
NMTC 3 \| US Bancorp
Variable Interest Entity [Line Items]
Financial Support to Other Entity	$ 3.8
NMTC 3 \| Unicom
Variable Interest Entity [Line Items]
Interest Rate on Loan	1.35%
Financial Support to Other Entity	$ 12.0
NMTC 4
Variable Interest Entity [Line Items]
Loan Amount	$ 6.7
Interest Rate on Loan	1.00%
NMTC 4 \| US Bancorp
Variable Interest Entity [Line Items]
Financial Support to Other Entity	$ 3.3
NMTC 4 \| Unicom
Variable Interest Entity [Line Items]
Interest Rate on Loan	0.73%
Financial Support to Other Entity	$ 9.8
NMTC 5
Variable Interest Entity [Line Items]
Loan Amount	$ 10.4
Interest Rate on Loan	1.00%
NMTC 5 \| Minimum
Variable Interest Entity [Line Items]
Interest Rate on Loan	0.67%
NMTC 5 \| Maximum
Variable Interest Entity [Line Items]
Interest Rate on Loan	1.24%
NMTC 5 \| US Bancorp
Variable Interest Entity [Line Items]
Financial Support to Other Entity	$ 5.1
NMTC 5 \| Unicom
Variable Interest Entity [Line Items]
Financial Support to Other Entity	$ 14.7

Variable Interest Entity, Financial or Other Support, Amount To Other Entity

No definition available.

Name:	gliba_VariableInterestEntityFinancialorOtherSupportAmountToOtherEntity
Namespace Prefix:	gliba_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Variable Interest Entity, Financial or Other Support, Interest Rate Percentage

+ References

No definition available.

+ Details

Name:	gliba_VariableInterestEntityFinancialorOtherSupportInterestRatePercentage
Namespace Prefix:	gliba_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of financial or other support the reporting entity has provided (explicitly or implicitly) to the Variable Interest Entity (VIE) that it was not previously contractually required to provide or that the reporting entity intends to provide, including, for example, situations in which the reporting entity assisted the VIE in obtaining another type of support.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=108788376&loc=SL6759159-111685

+ Details

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

- 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

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Period Type:	duration

- Details

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- Details

Name:	us-gaap_TypeOfArrangementAxis=gliba_NMTCTwoMember
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- Details

Name:	srt_RangeAxis=srt_MinimumMember
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- Details

Name:	srt_RangeAxis=srt_MaximumMember
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- Details

Name:	dei_LegalEntityAxis=gliba_USBancorpMember
Namespace Prefix:
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- Details

Name:	dei_LegalEntityAxis=gliba_CommunityDevelopmentEntitiesMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_TypeOfArrangementAxis=gliba_NMTCThreeMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	us-gaap_TypeOfArrangementAxis=gliba_NMTCFourMember
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- Details

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