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Earnings Per Unit (EPU) - Additional Information (Detail)
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Earnings Per Share [Abstract]      
Unvested restricted stock awards outstanding 463,774fr_NumberOfUnvestedRestrictedStockAwardsOutstandingIncludedInParticipatingSecurities 488,861fr_NumberOfUnvestedRestrictedStockAwardsOutstandingIncludedInParticipatingSecurities 288,627fr_NumberOfUnvestedRestrictedStockAwardsOutstandingIncludedInParticipatingSecurities