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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 35,669	$ 39,800	$ 76,303	$ 63,603
Net Income Allocable to Participating Securities	(59)	(89)	(118)	(149)
Net Income Available to Common Stockholders / Unitholders	$ 35,610	$ 39,711	$ 76,185	$ 63,454
Denominator:
Weighted Average Shares / Units - Basic	127,074	126,206	127,004	126,200
Performance Units (See Note 9) / Performance Units and certain Performance RLP Units (See Note 6)	192	283	185	272
Weighted Average Shares / Units - Diluted	127,266	126,489	127,189	126,472
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.28	$ 0.31	$ 0.60	$ 0.50
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 36,332	$ 40,689	$ 77,811	$ 65,003
Net Income Allocable to Participating Securities	(125)	(128)	(249)	(204)
Net Income Available to Common Stockholders / Unitholders	$ 36,207	$ 40,561	$ 77,562	$ 64,799
Denominator:
Weighted Average Shares / Units - Basic	129,081	128,831	129,075	128,824
Performance Units (See Note 9) / Performance Units and certain Performance RLP Units (See Note 6)	380	390	355	375
Weighted Average Shares / Units - Diluted	129,461	129,221	129,430	129,199
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.28	$ 0.31	$ 0.60	$ 0.50