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, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 42,446	$ 35,959	$ 156,580	$ 112,262
Net Income Allocable to Participating Securities	(48)	(59)	(170)	(177)
Net Income Available to Common Stockholders / Unitholders	$ 42,398	$ 35,900	$ 156,410	$ 112,085
Denominator:
Weighted Average Shares / Units - Basic	129,633	127,903	129,275	127,306
Performance Units (See Note 9) / Performance Units and certain Performance RLP Units (See Note 6)	89	198	87	189
Weighted Average Shares / Units - Diluted	129,722	128,101	129,362	127,495
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.33	$ 0.28	$ 1.21	$ 0.88
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 43,399	$ 36,639	$ 160,104	$ 114,450
Net Income Allocable to Participating Securities	(126)	(125)	(441)	(374)
Net Income Available to Common Stockholders / Unitholders	$ 43,273	$ 36,514	$ 159,663	$ 114,076
Denominator:
Weighted Average Shares / Units - Basic	131,668	129,914	131,345	129,357
Performance Units (See Note 9) / Performance Units and certain Performance RLP Units (See Note 6)	510	380	496	363
Weighted Average Shares / Units - Diluted	132,178	130,294	131,841	129,720
Basic and Diluted Earnings Per Share / Unit:
Earnings Per Share, Basic	$ 0.33	$ 0.28	$ 1.22	$ 0.88
Earnings Per Share, Diluted	$ 0.33	$ 0.28	$ 1.21	$ 0.88