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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 39,800	$ 45,209	$ 63,603	$ 81,501
Net Income Allocable to Participating Securities	(89)	(151)	(149)	(248)
Net Income Available to Common Stockholders / Unitholders	$ 39,711	$ 45,058	$ 63,454	$ 81,253
Denominator:
Weighted Average Shares / Units - Basic	126,206	123,616	126,200	121,741
Performance units and certain Performance LTIP Units (See Note 9)	283	469	272	417
Weighted Average Shares / Units - Diluted	126,489	124,085	126,472	122,158
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.31	$ 0.36	$ 0.50	$ 0.67
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 40,689	$ 46,382	$ 65,003	$ 83,825
Net Income Allocable to Participating Securities	(128)	(151)	(204)	(248)
Net Income Available to Common Stockholders / Unitholders	$ 40,561	$ 46,231	$ 64,799	$ 83,577
Denominator:
Weighted Average Shares / Units - Basic	128,831	126,832	128,824	125,289
Performance units and certain Performance LTIP Units (See Note 9)	390	469	375	417
Weighted Average Shares / Units - Diluted	129,221	127,301	129,199	125,706
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.31	$ 0.36	$ 0.50	$ 0.67