Earnings Per Share / Unit (EPS / EPU) - Computation of Basic and Diluted EPS / EPU (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 15,688	$ 2,373
Net Income Allocable to Participating Securities	(63)	(41)
Net Income Available to First Industrial Realty Trust, Inc.’s Common Stockholders	$ 15,625	$ 2,332
Denominator:
Weighted Average Shares / Units - Basic	110,793	110,310
LTIP Unit Awards (As Defined in Note 9)	192	365
Weighted Average Shares / Units - Diluted	110,985	110,675
Basic and Diluted EPS / EPU:
Net Income Available to Common Stockholders / Unitholders	$ 0.14	$ 0.02
First Industrial, L.P.
Numerator:
Net Income Available to Common Stockholders / Unitholders and Participating Securities	$ 16,281	$ 2,457
Net Income Allocable to Participating Securities	(63)	(41)
Net Income Available to Unitholders	$ 16,218	$ 2,416
Denominator:
Weighted Average Shares / Units - Basic	115,096	114,681
LTIP Unit Awards (As Defined in Note 9)	192	365
Weighted Average Shares / Units - Diluted	115,288	115,046
Basic and Diluted EPS / EPU:
Net Income Available to Common Stockholders / Unitholders	$ 0.14	$ 0.02

Net Income Available To Common Shareholders Basic Excluding Participating Securities

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Net Income Available to Unitholders Basic Excluding Participating Securities.

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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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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Amount of earnings (loss) distributed and earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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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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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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