Organization, Ownership and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) ft²	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) ft²	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019	Jun. 30, 2019 VIE	Jun. 30, 2019 building	Jun. 30, 2019 property	Jun. 30, 2019 ground_lease	Jun. 30, 2019 a	Jun. 30, 2019 property_partnership	Jun. 30, 2019 project	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($) VIE
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Lease-up properties occupancy percentage			95.00%
Lease-up properties occupancy duration			1 year
Common limited partnership interest in the Operating Partnership		2.00%		2.00%		2.00%									2.00%
Number of VIEs | VIE							2								3
VIE assets					$ 457,300										$ 615,400
VIE liabilities					30,900										45,100
Noncontrolling interest in VIE					192,908										192,363
Operating Lease, Lease Income	$ 197,629		$ 397,011
Leasing costs	2,650		4,407
Number of ground leases | ground_lease										4
Operating right of use ground lease asset					82,647									$ 82,938
Operating ground lease liabilities					87,082									87,409
Provision for bad debts	0	$ 5,641	0	$ 5,376
Rental income [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Provision for bad debts	200
Accounting Standards Update 2016-02 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Leasing costs	3,400		6,000
Cumulative adjustment														3,146
Allowance for deferred rent receivables					3,300
Accounting Standards Update 2016-02 [Member] | Property expense reimbursement [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating Lease, Lease Income	$ 3,100		$ 6,100
San Francisco, California [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | building								1
Office properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties								94	4
Rentable square feet | ft²	13,546,615		13,546,615
Area of land | a											59
Office properties [Member] | Washington [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | property									8
Office properties [Member] | Development project in San Francisco [Member] | San Francisco, California [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Area of real estate property | ft²	394,340		394,340
Development properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of property partnerships | property_partnership												3
Development properties [Member] | Washington [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | property									1
Development properties [Member] | Development project in San Francisco [Member] | San Francisco, California [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | property									1
Development sites [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | project													4
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					392,000										543,900
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					$ 187,000										$ 186,400
101 First LLC and 303 Second LLC [Member] | Development properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of property partnerships | property_partnership												2
Redwood LLC [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | property									2
Common general partnership interest in the Operating Partnership						93.00%
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%
Distributions in Excess of Earnings [Member] | Accounting Standards Update 2016-02 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Cumulative adjustment														$ 3,146