Organization and Basis of Presentation (Details Textual) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 ft²	Jun. 30, 2017 project	Jun. 30, 2017 building	Jun. 30, 2017 a	Jun. 30, 2017 VIE	Jun. 30, 2017 property	Dec. 31, 2016 USD ($) VIE
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Lease-up properties occupancy percentage	95.00%
Common general partnership interest in the Operating Partnership	97.90%	97.20%								97.50%
Common limited partnership interest in the Operating Partnership	2.10%	2.80%								2.50%
Number of VIEs | VIE								2		3
VIE assets			$ 431,300							$ 654,300
VIE liabilities			152,600							166,100
Noncontrolling interest in VIE			128,706							130,732
Net cash (used in) provided by investing activities	$ (216,018)	$ (39,069)
Restricted cash		258,100
Ground leases, future minimum payments receivable			253,900
101 First LLC and 303 Second LLC [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Common general partnership interest in the Operating Partnership	56.00%
Noncontrolling interest in VIE			122,400							124,300
Kilroy Realty Finance, Inc. [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Common general partnership interest in the Finance Partnership (percentage)	1.00%
Kilroy Realty, L.P. [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Percentage of limited partnership interest owned by Operating Partnership	99.00%
Net cash (used in) provided by investing activities	$ (216,018)	$ (39,069)
Redwood LLC [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Common general partnership interest in the Operating Partnership	93.00%
Office properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Rentable Square Feet (unaudited) | ft²				14,394,534
Number of Buildings						111			4
Area of land | a							52
Office properties [Member] | Washington [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Buildings | property									12
Development properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Rentable Square Feet (unaudited) | ft²				1,800,000
Number of Buildings					4				3
Development properties [Member] | San Francisco, California [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Rentable Square Feet (unaudited) | ft²				365,359
Development sites [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Buildings | project					6
Properties and development projects [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Property ownership percentage	100.00%
Real estate investment [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
VIE assets			$ 386,700							$ 588,600
Scenario, Previously Reported [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Net cash (used in) provided by investing activities	$ 304,500