Lease term.

No definition available.

Name:	gcnl_LeaseTerm
Namespace Prefix:	gcnl_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Land Parcels Held for Future Development

+ References

No definition available.

+ Details

Name:	gcnl_NumberofLandParcelsHeldforFutureDevelopment
Namespace Prefix:	gcnl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of real estate properties acquired.

+ References

No definition available.

+ Details

Name:	gcnl_NumberofRealEstatePropertiesAcquired
Namespace Prefix:	gcnl_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Property Interest Acquired

+ References

No definition available.

+ Details

Name:	gcnl_PropertyInterestAcquired
Namespace Prefix:	gcnl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Purchase price.

+ References

No definition available.

+ Details

Name:	gcnl_PurchasePrice
Namespace Prefix:	gcnl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of states the entity operates in as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Cash received for the sale of real estate that is not part of an investing activity during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfRealEstate
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

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

- Details

Name:	us-gaap_RealEstatePropertiesAxis=gcnl_IntangiblesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=gcnl_HealthSpringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate - Narrative (Details) $ in Thousands			1 Months Ended	9 Months Ended	12 Months Ended
Real Estate - Narrative (Details) $ in Thousands	Apr. 27, 2016 USD ($)	Mar. 17, 2016 USD ($) acquisition	Jan. 31, 2016 USD ($)	Sep. 30, 2016 USD ($) property parcel state	Dec. 31, 2015
Real Estate Properties [Line Items]
Number of properties \| property				75
Number of states \| state				20
Number of land parcels held for future development \| parcel				2
Purchase price				$ 3,000,000
Number of real estate asset acquired \| acquisition		2
Purchase price of property		$ 2,800
Restricted cash - real estate funds held for exchange			$ 47,000
Intangibles
Real Estate Properties [Line Items]
Lease Term				7 years 1 month	7 years 9 months 24 days
HealthSpring
Real Estate Properties [Line Items]
Purchase price of property				$ 41,300
Property interest acquired (percent)	90.00%
Payments to acquire property	$ 37,200