Acquisitions - 2016 Acquisitions (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) ft² building property	Jan. 31, 2014 ft²
Business Acquisition [Line Items]
Number of operating properties acquired | property	7
Rentable Square Feet (unaudited) | ft²	14,025,856	79,000
Accounts payable, accrued expenses and other liabilities	$ 1,122
Revenue contributed from 2016 acquired properties	5,200
Net income contributed from 2016 acquired properties	$ 1,700
1290-1300 Terra Bella Avenue, Mountain View, CA [Member]
Business Acquisition [Line Items]
Number of Buildings | building	1
Rentable Square Feet (unaudited) | ft²	114,175
Occupancy as of December 31, 2016 (unaudited)	100.00%
Purchase Price (in millions) (1)	$ 55,400
Accounts payable, accrued expenses and other liabilities	$ 200
8560-8590 West Sunset Blvd., West Hollywood, CA [Member]
Business Acquisition [Line Items]
Number of Buildings | building	4
Rentable Square Feet (unaudited) | ft²	178,699
Occupancy as of December 31, 2016 (unaudited)	87.50%
Purchase Price (in millions) (1)	$ 209,200
Accounts payable, accrued expenses and other liabilities	$ 100
1701 Page Mill Rd. and 3150 Porter Dr., Palo Alto, CA [Member]
Business Acquisition [Line Items]
Number of Buildings | building	2
Rentable Square Feet (unaudited) | ft²	165,585
Occupancy as of December 31, 2016 (unaudited)	100.00%
Purchase Price (in millions) (1)	$ 130,000
Series of individually immaterial business acquisitions [Member]
Business Acquisition [Line Items]
Number of Buildings | building	7
Rentable Square Feet (unaudited) | ft²	458,459
Purchase Price (in millions) (1)	$ 394,600