Investments in Real Estate and Real Estate Under Construction - Summary of acquisitions and build-to-suit transactions (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	$ 197,275
Land and land estate	21,251us-gaap_Land
Building and improvements	149,208
Lease in-place value	26,816
Office Building [Member] \| Auburn Hills, Michigan [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	40,025
Land and land estate	4,416
Building and improvements	30,012
Lease in-place value	5,597
Industrial property [Member] \| Houston, TX [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	28,650
Land and land estate	4,674
Building and improvements	19,540
Lease in-place value	4,436
Industrial property [Member] \| Brookshire, TX [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	22,450
Land and land estate	2,388
Building and improvements	16,614
Lease in-place value	3,448
Industrial property [Member] \| Canton, Mississippi [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	89,300
Land and land estate	5,077
Building and improvements	71,289
Lease in-place value	12,934
Land [Member] \| Venice, Florida [Member]
Investments in Real Estate and Real Estate Under Construction [Line Items]
Initial cost basis	16,850
Land and land estate	4,696
Building and improvements	11,753
Lease in-place value	$ 401

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 30

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 30

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

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- Definition

This element represents the amount of value allocated by a lessor (acquirer) to lease agreements which exist at acquisition of a leased property. Such amount may include the value assigned to existing tenant relationships and excludes the market adjustment component of the value assigned for above or below-market leases acquired.

+ References

No definition available.

+ Details

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- Definition

Aggregate of the carrying amounts as of the balance sheet date of investments in building and building improvements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(d))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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- Definition

Amount before accumulated depletion of real estate held for productive use, excluding land held for sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 45

-Paragraph 4

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6812-107765

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.13)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	debit
Period Type:	instant

- Details

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