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
Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 23,803	$ 36,292
Net Income Allocable to Participating Securities	(60)	(97)
Net Income Available to Common Stockholders / Unitholders	$ 23,743	$ 36,195
Denominator:
Weighted Average Shares / Units - Basic	126,194	119,846
Performance units and certain Performance LTIP Units (See Note 9)	262	365
Weighted Average Shares / Units - Diluted	126,456	120,211
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.19	$ 0.30
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 24,314	$ 37,443
Net Income Allocable to Participating Securities	(76)	(97)
Net Income Available to Common Stockholders / Unitholders	$ 24,238	$ 37,346
Denominator:
Weighted Average Shares / Units - Basic	128,818	123,729
Performance units and certain Performance LTIP Units (See Note 9)	360	365
Weighted Average Shares / Units - Diluted	129,178	124,094
Basic and Diluted Earnings Per Share / Unit:
Net Income Available to Common Stockholders / Unitholders	$ 0.19	$ 0.30

The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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