Segment Information - Schedule of Reconciliation of Net Income Attributable to Parent (Details) - USD ($) $ in Thousands		2 Months Ended	3 Months Ended		9 Months Ended
	Jul. 18, 2017	Sep. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Net income (loss) attributable to JBG SMITH Properties			$ (69,831)	$ 21,014	$ (57,851)	$ 49,344
Depreciation and amortization			43,951	31,377	109,726	98,291
Corporate and other			10,593	10,913	35,536	36,040
Third-party real estate services			21,178	4,779	30,362	14,272
Share-based compensation related to Formation Transaction			14,445	0	14,445	0
Transaction and other costs			104,095	1,528	115,173	1,528
Interest expense			15,309	13,028	43,813	38,662
Loss on extinguishment of debt			689	0	689	0
Income tax (benefit) expense			(1,034)	302	(317)	884
Third-party real estate services, including reimbursements			25,141	8,297	38,881	24,617
Other income			1,158	1,564	3,701	3,938
(Loss) income from unconsolidated real estate ventures			(1,679)	584	(1,365)	(952)
Interest and other (loss) income, net			(379)	749	1,366	2,292
Gain on bargain purchase			27,771	0	27,771	0
Net loss attributable to redeemable noncontrolling interests			8,160	0	2,481	0
NOI			79,223	71,747	218,741	209,126
JBG Companies
Business Acquisition [Line Items]
Transaction and other costs		$ 121,600		1,528		1,528
Gain on bargain purchase	$ 27,771		$ 27,771	$ 27,800	$ 27,800	$ 27,800