Earnings Per Share / Unit (EPS / EPU) - Additional Information (Detail) - shares	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Number Of Unvested Restricted Stock Awards Outstanding Included In Participating Securities	387,947	463,774	488,861

Number of unvested restricted stock awards outstanding included in participating securities.

No definition available.

Name:	fr_NumberOfUnvestedRestrictedStockAwardsOutstandingIncludedInParticipatingSecurities
Namespace Prefix:	fr_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant