Dispositions (Assets and liabilities related to dispositions) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Dispositions
Other assets	$ 52		$ 52		$ 1,357
Other liabilities	214		214		$ 3,620
Income from discontinued operations:
Total revenues	339	$ 118,939	693	$ 235,222
Total expenses	274	94,510	991	190,222
Income from discontinued operations before net gain on sale of real estate	65	24,429	(298)	45,000
Additional net gains on sale of real estate	618	0	618	2,267
JBG SMITH Properties spin-off transaction costs	0	(6,211)	0	(13,464)
Income from partially-owned entities	0	255	0	342
Pretax income from discontinued operations	683	18,473	320	34,145
Income tax expense	0	(362)	0	(716)
Income from discontinued operations	$ 683	$ 18,111	320	33,429
Cash flows related to discontinued operations:
Cash flows from operating activities			(1,781)	83,705
Cash flows from investing activities			$ 0	$ (52,740)