Dispositions (Assets and liabilities related to dispositions) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Dispositions
Other assets	$ 74		$ 74		$ 1,357
Other liabilities	205		205		$ 3,620
Income (loss) from discontinued operations:
Total revenues	174	$ 25,747	867	$ 260,969
Total expenses	113	21,708	1,104	211,930
Income from discontinued operations before net gain on sale of real estate	61	4,039	(237)	49,039
JBG SMITH Properties (JBGS) spin-off transaction costs	0	(53,581)	0	(67,045)
Additional net gains on sale of real estate	0	1,530	618	3,797
Income from partially-owned entities	0	93	0	435
Pretax income (loss) from discontinued operations	61	(47,919)	381	(13,774)
Income tax expense	0	(11)	0	(727)
Income (loss) from discontinued operations	$ 61	$ (47,930)	381	(14,501)
Cash flows related to discontinued operations:
Cash flows from operating activities			(1,751)	39,581
Cash flows from investing activities			$ 0	$ (48,377)