Organization, Ownership and Basis of Presentation - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) property_partnership	Mar. 31, 2019 ground_lease	Mar. 31, 2019	Mar. 31, 2019 project	Mar. 31, 2019 tenant	Mar. 31, 2019 a	Mar. 31, 2019 USD ($)	Mar. 31, 2019 building	Mar. 31, 2019 VIE	Mar. 31, 2019 property	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($) VIE	Mar. 31, 2018 USD ($) tenant
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%	2.10%
Number of VIEs | VIE									2			3
VIE assets							$ 452,400					$ 615,400
VIE liabilities							32,100					45,100
Noncontrolling interest in VIE							190,245					192,363
Leasing costs	$ 1,757
Number of Ground Leases | ground_lease		4
Operating right of use ground lease asset							82,794				$ 82,938
Operating ground lease liabilities							87,247				87,409
Accounting Standards Update 2016-02 [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Operating Lease, Lease Income	3,000
Leasing costs	$ 2,600
Cumulative adjustment											3,146
Allowance for deferred rent receivables							3,500						$ 300
Number of Tenants | tenant													3
San Francisco, California [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Buildings | building								1
Office properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Buildings								94		4
Area of land | a						59
Number of Tenants | tenant					473
Office properties [Member] | Washington [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Buildings | property										8
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 Buildings | property										1
Development sites [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of Buildings | 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							396,500					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												$ 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 Buildings | building								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%
100 First LLC & 303 Second LLC [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling interest in VIE							$ 184,300
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