Number of tenants.

No definition available.

Name:	kbsriii_NumberOfTenants
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- Definition

Percentage of Real Estate Portfolio Occupied

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	instant

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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Balance Type:	na
Period Type:	duration

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of excess of rental income recognized over rental payment required by lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Balance Type:	credit
Period Type:	duration

- Definition

The charge against earnings in the period to reduce the carrying amount of real property to fair value.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of incentive granted by lessor to lessee.

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Term of lessor's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 30
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-Section 50
-Paragraph 3
-Subparagraph (a)(3)
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Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
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

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

- Definition

This element represents money paid in advance to protect the provider of a product or service, such as a lessor, against damage or nonpayment by the buyer or tenant (lessee) during the term of the agreement. Such damages may include physical damage to the property, theft of property, and other contractual breaches. Security deposits held may be interest or noninterest bearing.

+ References

No definition available.

+ Details

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

- Details

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- Details

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Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_GeographicConcentrationRiskMember
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Data Type:	na
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- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_OfficeBuildingMember
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Balance Type:
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- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=kbsriii_TheAlmadenMember
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REAL ESTATE - Additional Information (Details) $ in Thousands, ft² in Millions	12 Months Ended
	Dec. 31, 2025 USD ($) ft² property tenant	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Real Estate Properties [Line Items]
Rentable square feet \| ft²	5.6
Percentage of portfolio occupied	77.10%
Deferred rent recognized	$ 6,104	$ 8,553	$ 7,635
Deferred rent receivables	92,300	88,300
Incentive to lessee	16,300	16,600
Impairment of real estate	65,475	6,847	45,459
Gain from extinguishment of debt	$ 0	56,372	0
60 South Sixth
Real Estate Properties [Line Items]
Impairment of real estate		6,800
201 Spear Street
Real Estate Properties [Line Items]
Impairment of real estate			$ 45,500
Illinois \| Assets, Total \| Geographic Concentration Risk
Real Estate Properties [Line Items]
Concentration risk, percentage	23.90%
California \| Assets, Total \| Geographic Concentration Risk
Real Estate Properties [Line Items]
Concentration risk, percentage	19.90%
Texas \| Assets, Total \| Geographic Concentration Risk
Real Estate Properties [Line Items]
Concentration risk, percentage	11.30%
Other liabilities, at fair value
Real Estate Properties [Line Items]
Security deposit liability	$ 7,100	$ 8,400
Maximum
Real Estate Properties [Line Items]
Operating leases, term of contract	13 years 6 months
Weighted Average
Real Estate Properties [Line Items]
Operating leases, term of contract	5 years 3 months 18 days
Office Building
Real Estate Properties [Line Items]
Number of real estate properties \| property	12
Number of Tenants \| tenant	350
Office Building \| The Almaden
Real Estate Properties [Line Items]
Impairment of real estate	$ 28,500
Office Building \| Towers at Emeryville
Real Estate Properties [Line Items]
Impairment of real estate	16,300
Office Building \| 60 South Sixth
Real Estate Properties [Line Items]
Impairment of real estate	$ 20,700