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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 78,311	$ 30,911	$ 141,914	$ 112,412
Net Income Allocable to Participating Securities	(170)	(101)	(319)	(349)
Net Income Available to Common Stockholders / Unitholders	$ 78,141	$ 30,810	$ 141,595	$ 112,063
Denominator:
Weighted Average Shares / Units - Basic	126,480	125,768	126,295	123,098
Performance units and certain Performance LTIP Units (See Note 9)	303	362	283	399
Weighted Average Shares / Units - Diluted	126,783	126,130	126,578	123,497
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.62	$ 0.24	$ 1.12	$ 0.91
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 79,969	$ 31,508	$ 144,972	$ 115,333
Net Income Allocable to Participating Securities	(249)	(101)	(453)	(349)
Net Income Available to Common Stockholders / Unitholders	$ 79,720	$ 31,407	$ 144,519	$ 114,984
Denominator:
Weighted Average Shares / Units - Basic	128,837	128,526	128,829	126,380
Performance units and certain Performance LTIP Units (See Note 9)	419	362	390	399
Weighted Average Shares / Units - Diluted	129,256	128,888	129,219	126,779
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.62	$ 0.24	$ 1.12	$ 0.91