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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 51,936	$ 35,669	$ 114,134	$ 76,303
Net Income Allocable to Participating Securities	(61)	(59)	(122)	(118)
Net Income Available to Common Stockholders / Unitholders	$ 51,875	$ 35,610	$ 114,012	$ 76,185
Denominator:
Weighted Average Shares / Units - Basic	129,098	127,074	129,093	127,004
Performance Units (See Note 9) / Performance Units and certain Performance RLP Units (See Note 6)	89	192	86	185
Weighted Average Shares / Units - Diluted	129,187	127,266	129,179	127,189
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.40	$ 0.28	$ 0.88	$ 0.60
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 53,140	$ 36,332	$ 116,705	$ 77,811
Net Income Allocable to Participating Securities	(155)	(125)	(315)	(249)
Net Income Available to Common Stockholders / Unitholders	$ 52,985	$ 36,207	$ 116,390	$ 77,562
Denominator:
Weighted Average Shares / Units - Basic	131,188	129,081	131,180	129,075
Performance Units (See Note 9) / Performance Units and certain Performance RLP Units (See Note 6)	516	380	489	355
Weighted Average Shares / Units - Diluted	131,704	129,461	131,669	129,430
Basic and Diluted Earnings Per Share / Unit:
Earnings Per Share, Basic	$ 0.40	$ 0.28	$ 0.89	$ 0.60
Earnings Per Share, Diluted	$ 0.40	$ 0.28	$ 0.88	$ 0.60