Transactions With Parkway Properties, Inc. (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Acquisition and merger costs	$ 188	$ 1,700	$ 24,500
Revenue contributed from the merger			68,700
Net income contributed from the merger			9,000
Spin-off
Business Acquisition [Line Items]
Transaction costs included in discontinued operations			$ 6,300