Rental Property - Summary (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Components of rental property
Total rental property, net	$ 1,628,245us-gaap_RealEstateInvestmentPropertyNet	$ 1,558,080us-gaap_RealEstateInvestmentPropertyNet
Accumulated depreciation	117,106	105,789
Deferred leasing intangibles
Components of rental property
Total rental property, net	254,155	247,904
Accumulated amortization	159,206	146,026
Land
Components of rental property
Total rental property, net	202,930	191,238
Building
Components of rental property
Total rental property, net	1,093,054	1,042,086
Accumulated depreciation	82,836	75,116
Tenant improvements
Components of rental property
Total rental property, net	22,175	22,619
Accumulated depreciation	22,358	20,943
Building and land improvements
Components of rental property
Total rental property, net	55,931	54,233
Accumulated depreciation	$ 11,912	$ 9,730

For an unclassified balance sheet, the accumulated amortization, as of the reporting date, which represents the periodic charge to earnings of initial direct costs which have been deferred and are being allocated over the lease term in proportion to the recognition of rental income.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6453741&loc=d3e40879-112712

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=6748888&loc=d3e40588-112709

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- Definition

The cumulative amount of depreciation for real estate property held for investment purposes.

+ 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(3))

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 7

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Amount of real estate investment property, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

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