Dispositions of Real Estate and Discontinued Operations - Shoreline Technology Center (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings		$ 335,709	$ 462,242	$ 0
Shoreline Technology Center
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings	$ 1,000,000
Gain (loss) on sale of assets	$ 726,000