REAL ESTATE HELD FOR SALE - Revenue and Expenses of Real Estate Sales (Details) - Disposed of by Sale - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Revenues
Rental income	$ 1,070	$ 28,551
Other operating income	236	3,198
Total revenue	1,306	31,749
Expenses
Operating, maintenance, and management	846	6,894
Real estate taxes and insurance	117	3,899
Asset management fees to affiliate	129	2,001
General and administrative expenses	50	0
Depreciation and amortization	0	12,639
Interest expense	0	7,409
Total expenses	$ 1,142	$ 32,842

Disposal Group, Including Discontinued Operation, Asset Management Costs

No definition available.

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

- Definition

Disposal Group, Including Discontinued Operation, Costs and Expenses

+ References

No definition available.

+ Details

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

- Definition

Disposal Group, Including Discontinued Operation, Real Estate Taxes and Insurance

+ References

No definition available.

+ Details

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

- Definition

Amount of depreciation and amortization expense attributable to disposal group, including, but not limited to, discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721673-107760

+ Details

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

- Definition

Amount of general and administrative expense attributable to disposal group, including, but not limited to, discontinued operation.

+ References

+ Details

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

- Definition

Amount of interest expense attributable to disposal group, including, but not limited to, discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section S99
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=26872618&loc=d3e7436-122677

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109222160&loc=d3e1063-107759

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721673-107760

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109222160&loc=d3e1060-107759

+ Details

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

- Definition

Amount of operating expense attributable to disposal group, including, but not limited to, discontinued operation.

+ References

+ Details

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

- Definition

Amount of other income attributable to disposal group, including, but not limited to, discontinued operation.

+ References

+ Details

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

- Definition

Amount of rental income attributable to disposal group, including, but not limited to, discontinued operation.

+ References

+ Details

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

- Definition

Amount of revenue attributable to disposal group, including, but not limited to, discontinued operation.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupDisposedOfBySaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: