Acquisitions (Details) $ in Thousands			9 Months Ended
	Jun. 01, 2018 USD ($)	Jan. 31, 2018 USD ($) ft²	Sep. 30, 2018 USD ($) building
Assets
Land and improvements			$ 50,928
Buildings and improvements			59,123
Deferred leasing costs and acquisition-related intangible assets			4,470
Total assets acquired			114,521
Liabilities
Deferred revenue and acquisition-related intangible liabilities (3)			3,521
Total liabilities assumed			3,521
Net assets and liabilities acquired			111,000
Below market lease, acquired			$ 3,500
Acquired finite lived intangible liabilities weighted average useful life			9 years 9 months
In-place leases [Member]
Assets
Deferred leasing costs and acquisition-related intangible assets			$ 3,800
Liabilities
Acquired finite-lived intangible assets, weighted average useful life			2 years 7 months
Deferred leasing costs and acquisition-related intangible assets, net [Member]
Assets
Deferred leasing costs and acquisition-related intangible assets			$ 700
Liabilities
Acquired finite-lived intangible assets, weighted average useful life			3 years 6 months
345, 347 & 349 Oyster Point Boulevard, South San Francisco, CA [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Number of Buildings | building			3
Rentable Square Feet (unaudited) | ft²		145,530
Purchase Price (in millions)		$ 111,000
Kilroy Oyster Point [Member]
Schedule of Asset Acquisitions, by Acquisition [Line Items]
Purchase Price (in millions)	$ 308,200
Liabilities
Total liabilities assumed	$ 40,600