Dispositions (Assets and liabilities related to dispositions) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Dispositions
Real estate, net	$ 0		$ 0		$ 3,222,720
Other assets	1,774		1,774		345,893
Assets related to discontinued operations	1,774		1,774		3,568,613
Mortgages payable, net	0		0		1,165,015
Other liabilities	3,602		3,602		94,428
Liabilities related to discontinued operations	3,602		3,602		$ 1,259,443
(Loss) income from discontinued operations:
Total revenues	25,747	$ 134,912	260,969	$ 392,108
Total expenses	21,708	109,506	211,930	331,377
Income from discontinued operations before net gain on sale of real estate	4,039	25,406	49,039	60,731
JBG SMITH Properties spin-off transaction costs	(53,581)	(2,739)	(67,045)	(4,597)
Net gains on sale of real estate and a lease position	1,530	2,864	3,797	5,074
Income (loss) from partially owned assets	93	316	435	(3,363)
Impairment losses	0	(465)	0	(161,165)
Pretax (loss) income from discontinued operations	(47,919)	25,382	(13,774)	(103,320)
Income tax expense	(11)	(302)	(727)	(884)
(Loss) income from discontinued operations	$ (47,930)	$ 25,080	(14,501)	(104,204)
Cash flows related to discontinued operations:
Cash flows from operating activities			39,581	107,797
Cash flows from investing activities			$ (48,377)	$ (176,374)