Investments in Real Estate - Dispositions (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) ft²	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) ft²	Sep. 30, 2016 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²	3,582,375		3,582,375
Gain Recorded (in thousands)	$ 0	$ 0	$ 19,237	$ 11,563
Dispositions
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²	563,217		563,217
Contractual Sales Price	$ 65,625		$ 65,625
Gain Recorded (in thousands)	$ 19,237
Dispositions | 9375 Archibald Avenue
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²	62,677		62,677
Contractual Sales Price	$ 6,875		$ 6,875
Gain Recorded (in thousands)	$ 2,668
Dispositions | 2535 Midway Drive
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²	373,744		373,744
Contractual Sales Price	$ 40,050		$ 40,050
Gain Recorded (in thousands)	$ 15,974
Dispositions | 2811 Harbor Boulevard
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Rentable Square Feet | ft²	126,796		126,796
Contractual Sales Price	$ 18,700		$ 18,700
Gain Recorded (in thousands)	$ 595