Earnings Per Share / Unit (EPS / EPU) - Computation of Basic and Diluted EPS / EPU (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 83,727	$ 35,959	$ 35,669	$ 40,634	$ 96,861	$ 78,311	$ 39,800	$ 23,803	$ 195,989	$ 238,775	$ 163,239
Net Income Allocable to Participating Securities	(137)	(59)	(59)	(59)	(199)	(170)	(89)	(60)	(314)	(518)	(513)
Net Income Available to Common Stockholders / Unitholders	$ 83,590	$ 35,900	$ 35,610	$ 40,575	$ 96,662	$ 78,141	$ 39,711	$ 23,743	$ 195,675	$ 238,257	$ 162,726
Denominator:
Weighted Average Shares/Units - Basic	128,919	127,903	127,074	126,934	126,682	126,480	126,206	126,194	127,711	126,392	123,804
Performance Units/Performance Units and certain Performance RLP Units									193	299	387
Weighted Average Shares / Units - Diluted	129,125	128,101	127,266	127,111	127,030	126,783	126,489	126,456	127,904	126,691	124,191
Basic Earnings Per Share / Unit:
Net Income Available to Common Stockholders/Unitholders	$ 0.65	$ 0.28	$ 0.28	$ 0.32	$ 0.76	$ 0.62	$ 0.31	$ 0.19	$ 1.53	$ 1.89	$ 1.31
Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders/Unitholders									$ 1.53	$ 1.88	$ 1.31
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 85,484	$ 36,639	$ 36,332	$ 41,479	$ 98,656	$ 79,969	$ 40,689	$ 24,314	$ 199,934	$ 243,628	$ 167,246
Net Income Allocable to Participating Securities	(289)	(125)	(125)	(123)	(279)	(249)	(128)	(76)	(662)	(732)	(513)
Net Income Available to Common Stockholders / Unitholders	$ 85,195	$ 36,514	$ 36,207	$ 41,356	$ 98,377	$ 79,720	$ 40,561	$ 24,238	$ 199,272	$ 242,896	$ 166,733
Denominator:
Weighted Average Shares/Units - Basic	130,929	129,914	129,081	129,070	128,837	128,837	128,831	128,818	129,752	128,831	126,921
Performance Units/Performance Units and certain Performance RLP Units									375	410	387
Weighted Average Shares / Units - Diluted	131,339	130,294	129,461	129,400	129,308	129,256	129,221	129,178	130,127	129,241	127,308
Basic Earnings Per Share / Unit:
Net Income Available to Common Stockholders/Unitholders	$ 0.65	$ 0.28	$ 0.28	$ 0.32	$ 0.76	$ 0.62	$ 0.31	$ 0.19	$ 1.54	$ 1.89	$ 1.31
Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders/Unitholders									$ 1.53	$ 1.88	$ 1.31