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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 35,959	$ 78,311	$ 112,262	$ 141,914
Net Income Allocable to Participating Securities	(59)	(170)	(177)	(319)
Net Income Available to Common Stockholders / Unitholders	$ 35,900	$ 78,141	$ 112,085	$ 141,595
Denominator:
Weighted Average Shares / Units - Basic	127,903	126,480	127,306	126,295
Performance Units (See Note 9) / Performance Units and certain Performance RLP Units (See Note 6)	198	303	189	283
Weighted Average Shares / Units - Diluted	128,101	126,783	127,495	126,578
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.28	$ 0.62	$ 0.88	$ 1.12
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 36,639	$ 79,969	$ 114,450	$ 144,972
Net Income Allocable to Participating Securities	(125)	(249)	(374)	(453)
Net Income Available to Common Stockholders / Unitholders	$ 36,514	$ 79,720	$ 114,076	$ 144,519
Denominator:
Weighted Average Shares / Units - Basic	129,914	128,837	129,357	128,829
Performance Units (See Note 9) / Performance Units and certain Performance RLP Units (See Note 6)	380	419	363	390
Weighted Average Shares / Units - Diluted	130,294	129,256	129,720	129,219
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.28	$ 0.62	$ 0.88	$ 1.12