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Investment in Real Estate (Details 4) (Level 3 Fair Value Measurements [Member], 3rd Party Pricing [Member], USD $) In Thousands, unless otherwise specified | 6 Months Ended
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Jun. 30, 2012
Level 3 Fair Value Measurements [Member] | 3rd Party Pricing [Member] |
Quantitative information about Level 3 fair value measurements |
Fair Value Measurements | $ 24,069
Fair value inputs third party purchase contract or letters of intent |

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- Definition Fair value inputs third party purchase contract or letters of intent. + References No definition available. + Details
Name: | fr_FairValueInputsThirdPartyPurchaseContractOrLettersOfIntent
Namespace Prefix: | fr_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | us-gaap_FairValueInputsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration