Debt Amount Allocated to for Leasing Costs, Commissions, and Tenant Improvements

No definition available.

Name:	kbsriii_DebtAmountAllocatedToForLeasingCostsCommissionsAndTenantImprovements
Namespace Prefix:	kbsriii_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt Instrument, Extension Period

+ References

No definition available.

+ Details

Name:	kbsriii_DebtInstrumentExtensionPeriod
Namespace Prefix:	kbsriii_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Number of Extensions

+ References

No definition available.

+ Details

Name:	kbsriii_DebtInstrumentNumberOfExtensions
Namespace Prefix:	kbsriii_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Percent of Outstanding balance under Guarantees

+ References

No definition available.

+ Details

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Namespace Prefix:	kbsriii_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: 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(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: 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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

- Definition

Amount of unused borrowing capacity under the long-term financing arrangement that is available to the entity as of the balance sheet date.

+ References

+ Details

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

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ 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(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: 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(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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

- Definition

Period between issuance and maturity of long-term debt, 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=kbsriii_AccentureTowerRevolvingLoanMember
Namespace Prefix:
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Balance Type:
Period Type:

- Details

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SUBSEQUENT EVENTS - Financings (Details)				1 Months Ended	9 Months Ended
SUBSEQUENT EVENTS - Financings (Details)	Nov. 03, 2020 USD ($) extension	Nov. 02, 2020 USD ($) extension	Nov. 03, 2017 USD ($) extension	Nov. 13, 2020	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Subsequent Event [Line Items]
Amount drawn					$ 1,496,682,000	$ 1,466,376,000
Portfolio Loan Facility \| Secured Debt
Subsequent Event [Line Items]
Long-term debt, term			3 years
Maximum borrowing capacity			$ 1,010,000,000.00		911,000,000.0
Loan, amount outstanding			$ 757,500,000		$ 683,200,000
Number of extensions \| extension			2
Extension period			12 months		1 year
Portfolio Loan Facility \| Secured Debt \| Revolving Credit Facility
Subsequent Event [Line Items]
Maximum borrowing capacity					$ 227,800,000
Loan, amount outstanding			$ 252,500,000
Unused borrowing capacity, amount					$ 227,800,000
Subsequent Event \| Accenture Tower Revolving Loan \| Secured Debt
Subsequent Event [Line Items]
Long-term debt, term		3 years
Maximum borrowing capacity		$ 375,000,000.0
Loan, amount outstanding		281,300,000
Amount drawn		$ 281,300,000
Number of extensions \| extension		2
Extension period		12 months
Basis spread on variable rate		2.25%
Percent of outstanding balance under guarantees		25.00%
Subsequent Event \| Accenture Tower Revolving Loan \| Secured Debt \| Revolving Credit Facility
Subsequent Event [Line Items]
Loan, amount outstanding		$ 93,700,000
Unused borrowing capacity, amount		93,700,000
Amount to be used for tenant improvements and lease commissions		30,000,000.0
Subsequent Event \| Portfolio Loan Facility
Subsequent Event [Line Items]
Extinguishment of debt, amount		$ 210,300,000
Subsequent Event \| Portfolio Loan Facility \| Secured Debt
Subsequent Event [Line Items]
Extension period				1 year
Subsequent Event \| Modified Portfolio Loan Facility \| Secured Debt
Subsequent Event [Line Items]
Maximum borrowing capacity	$ 630,600,000
Loan, amount outstanding	$ 472,900,000
Number of extensions \| extension	1
Extension period	12 years
Subsequent Event \| Modified Portfolio Loan Facility \| Secured Debt \| Revolving Credit Facility
Subsequent Event [Line Items]
Loan, amount outstanding	$ 157,700,000