Investments in Real Estate (Details) (USD $)	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Real Estate Properties [Line Items]
Investment in new properties	$ 364,200,000
Announced definitive purchase agreements	544,000,000
Capitalized costs on existing properties	1,900,000	1,600,000
Re-leasing costs	649,000	636,000
Building and tenant improvements	1,200,000	966,000
Crest's property inventory, number of properties	3		3
Crest's property inventory net book value	2,900,000		3,000,000
Intangible value of above-market leases	106,551,000		26,221,000
Intangible value of below-market leases	5,125,000		3,452,000
Real Estate Investments [Member]
Real Estate Properties [Line Items]
Investment in new properties	364,200,000	289,000,000
Number of new properties	36	21
Weighted average contractual lease rate (in hundredths)	7.60%	7.60%
Different U.S. State of location	19	7
Leasable square feet (in square feet)	3,400,000	501,000
Leased percentage (in hundredths)	100.00%	100.00%
Average lease term (in years)	15.5	19.2
Acquisition transaction costs	913,000	88,000
Announced Real Estate Purchase Agreements [Member]
Real Estate Properties [Line Items]
Number of new properties	33
Different U.S. State of location	17
Leasable square feet (in square feet)	3,800,000
Announced definitive purchase agreements	544,000,000
Announced definitive purchase agreement amount included in current period real estate investments	336,200,000
Announced definitive purchase agreement locations included in current period real estate investments	22
Tenant industries	11
Average lease term (in years)	11
Real Estate Investments With Existing Leases [Member]
Real Estate Properties [Line Items]
Number of new properties	22
Intangible value of the in-place leases	64,500,000
Intangible value of above-market leases	18,600,000
Intangible value of below-market leases	$ 1,900,000

Value of announced and signed definitive purchase agreements for business acquisitions for investments made within the period.

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- Definition

The number of real estate properties owned as of the balance sheet date for announced and signed definitive purchase agreements for business acquisitions of investments made within the period.

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Value of announced and signed definitive purchase agreements for business acquisitions.

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- Definition

Average period of time covered by real estate lease contracts.

+ Details

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- Definition

Average period of time covered by real estate lease contracts.

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- Definition

Portion of real estate properties with existing tenant lease agreements in place expressed as a percentage of total.

+ Details

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- Definition

The number of new real estate properties invested in as of the balance sheet date.

+ Details

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- Definition

The number of states in which the real estate properties acquired during the period operate.

+ Details

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- Definition

Amount of re-leasing costs related to real estate investments during the period.

+ Details

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- Definition

The amount of square footage related to a real estate properties acquired during the period.

+ Details

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- Definition

Subsidiary entity number of real estate properties owned as of the balance sheet date.

+ Details

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- Definition

The net book value of real estate property held for investment purposes of a wholly owned subsidiary.

+ Details

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- Definition

Number of different industries of tenants in current lease agreements for real estate acquired during the period.

+ Details

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- Definition

Computed as estimated contractual net operating income (in a net-leased property that is equal to the aggregate base rent or, in the case of properties under development, the estimated aggregate base rent under the lease) for the first year of each lease, divided by the estimated total cost of the properties

+ Details

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- Definition

Amount of direct costs of the business combination including legal, accounting, and other costs incurred to consummate the business acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 51
-Subparagraph d
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 24
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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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.

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This element represents the identifiable intangible asset established upon acquisition based on a favorable difference between the terms of an acquired lease and the current market terms for that lease at the acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 37
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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 210.5-02.15)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

This element represents a liability associated with the acquisition of an off-market lease when the terms of the lease are unfavorable to the market terms for the lease at the date of acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 141
-Paragraph 37
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB
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-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

Carrying amount as of the balance sheet date of improvements made to the property and capitalized after acquisition.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 970
-SubTopic 360
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-28)
-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
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-Paragraph c
-Subparagraph Schedule III
-Article 5

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-Publisher SEC
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-Paragraph 6
-Subparagraph (SX 210.5-04.(c) Schedule III)
-URI http://asc.fasb.org/extlink&oid=6882300&loc=d3e5864-122674

+ Details

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- Definition

Amount of improvements made to real estate investments during the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 360
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-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6882300&loc=d3e5864-122674

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- Definition

Investments in real estate held solely for investment purposes (income production and capital appreciation).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 7
-Section 03
-Paragraph 1
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-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 1
-Subparagraph (SX 210.7-03.1(d))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ Details

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