Discount on Financing Receivable Originated

No definition available.

Name:	kbsriii_DiscountOnFinancingReceivableOriginated
Namespace Prefix:	kbsriii_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Face Value of Financing Receivable Originated

+ References

No definition available.

+ Details

Name:	kbsriii_FaceValueOfFinancingReceivableOriginated
Namespace Prefix:	kbsriii_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Interest Income Components

+ References

No definition available.

+ Details

Name:	kbsriii_InterestIncomeComponentsAbstract
Namespace Prefix:	kbsriii_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Mortgage Loans On Real Estate Commercial And Consumer, Gross

+ References

No definition available.

+ Details

Name:	kbsriii_MortgageLoansOnRealEstateCommercialAndConsumerGross
Namespace Prefix:	kbsriii_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of Financing Receivables Originated

+ References

No definition available.

+ Details

Name:	kbsriii_NumberOfFinancingReceivablesOriginated
Namespace Prefix:	kbsriii_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Origination Costs On Real Estate Loan Receivable

+ References

No definition available.

+ Details

Name:	kbsriii_OriginationCostsOnRealEstateLoanReceivable
Namespace Prefix:	kbsriii_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Origination of Financing Receivable

+ References

No definition available.

+ Details

Name:	kbsriii_OriginationOfFinancingReceivableAbstract
Namespace Prefix:	kbsriii_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Real Estate Loans Receivable

+ References

No definition available.

+ Details

Name:	kbsriii_RealEstateLoansReceivableRollForward
Namespace Prefix:	kbsriii_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The sum of the periodic adjustments of the differences between securities' face values and purchase prices that are charged against earnings. This is called accretion if the security was purchased at a discount and amortization if it was purchased at premium. As a noncash item, this element is an adjustment to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

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

- Definition

The net increase(decrease) in interest income during the period representing the allocation of deferred loan origination fees less deferred loan origination costs using the effective interest method over the term of the debt arrangement to which they pertain taking into account the effect of prepayments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 35
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=121604886&loc=d3e8622-111531

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

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

- Definition

Interest and fee income related to commercial loans including industrial and agricultural, real estate (commercial and residential, construction and development), trade financing, and lease financing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.1)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

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

- Definition

Interest and fee income generated from loans secured by commercial properties. Examples of properties commonly securing commercial real estate loans may include office buildings, apartment buildings, shopping centers, industrial property, and hotels.

+ References

+ Details

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

- Definition

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_InterestReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(c))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_MortgageLoansOnRealEstateCommercialAndConsumerNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(11))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

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

- Definition

Yield on the receivable, on which interest has been imputed, as calculated from its issuance value or purchase price. The calculated effective interest rate considers factors such as the issued face value or price paid for the receivable, the time period between payments, and the time until maturity [full receipt] of the receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

+ Details

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

- References

No definition available.

+ Details

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

REAL ESTATE LOAN RECEIVABLE - Schedules (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) numberOfLoans
Receivables [Abstract]
Number of real estate loans receivables originated \| numberOfLoans					1
Origination of Financing Receivable [Abstract]
Outstanding Principal Balance					$ 150,213
Book Value	$ 148,290		$ 148,290		148,290
Annualized Effective Interest Rate			5.34%
Real Estate Loans Receivable [Roll Forward]
Real estate loan receivable, net - December 31, 2019			$ 0
Face value of real estate loan receivable originated			150,213
Discount on real estate loan receivable originated			(2,535)
Accretion of origination discount	674		1,230
Origination costs on real estate loan receivable			120	$ 0
Amortization of origination costs on real estate loan receivable	32		58
Provision for credit loss	0	$ 0	(680)	$ 0
Real estate loan receivable, net - September 30, 2020	148,290		148,290
Interest Income Components [Abstract]
Contractual interest income	1,387		2,064
Accretion of origination discount	674		1,230
Amortization of origination costs	32		58
Interest income from real estate loan receivable	$ 2,029		$ 3,236
Interest receivable					$ 500