Organization, Ownership and Basis of Presentation - Narrative (Details) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) ft² a building project VIE property entity property_partnership	Jun. 30, 2019	Dec. 31, 2019 USD ($) VIE entity property_partnership
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
Assets	$ 9,658,665		$ 8,900,094
Liabilities	4,405,076		4,329,236
Noncontrolling interest in VIE	$ 197,796		$ 195,431
San Francisco, California [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | building	1
Washington [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | property	1
Stabilized office properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | building	114
Area of undeveloped land | a	61
Rentable square feet | ft²	14,327,872
Stabilized 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
Development properties [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | property	2
Number of property partnerships | property_partnership	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 | ft²	750,370
Development properties [Member] | San Diego, California [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Rentable square feet | ft²	95,871
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
Office properties owned by consolidated property partnerships [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | property	4
Development sites [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of properties | project	5
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%
101 First LLC and 303 Second LLC [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Company owned general partnership interest	56.00%
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
Company owned general partnership interest	93.00%
Operating Partnership [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ownership interest (percent)	98.30%	98.00%	98.10%
Non-affiliated investors and certain of our executive officers and directors [Member] | Operating Partnership [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ownership interest (percent)	1.70%	2.00%	1.90%
Kilroy Realty Finance, Inc. [Member] | Finance Partnership [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%
Operating Partnership [Member] | Finance Partnership [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ownership interest (percent)	99.00%
Variable Interest Entity, Primary Beneficiary [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Number of property partnerships | property_partnership	2		2
Number of VIEs | VIE	4		4
Number of entities established | entity	2		2
Assets	$ 686,400		$ 676,700
Liabilities	42,700		40,100
Variable Interest Entity, Primary Beneficiary [Member] | Real estate investment [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Assets	598,000		598,000
Variable Interest Entity, Primary Beneficiary [Member] | 101 First LLC and 303 Second LLC [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling interest in VIE	$ 192,100		$ 189,600