Schedule III - Real Estate Investments (Summary of Historical Cost and Accumulated Depreciation) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property
Balance, beginning of period	$ 905,735us-gaap_RealEstateGrossAtCarryingValue	$ 734,828us-gaap_RealEstateGrossAtCarryingValue	$ 555,586us-gaap_RealEstateGrossAtCarryingValue
Disposals	(54)us-gaap_RealEstateCostOfRealEstateSold		(794)us-gaap_RealEstateCostOfRealEstateSold
Additions (acquisitions and improvements)	271,901us-gaap_RealEstateOtherAcquisitions	170,907us-gaap_RealEstateOtherAcquisitions	180,036us-gaap_RealEstateOtherAcquisitions
Balance, end of period	1,177,582us-gaap_RealEstateGrossAtCarryingValue	905,735us-gaap_RealEstateGrossAtCarryingValue	734,828us-gaap_RealEstateGrossAtCarryingValue
Accumulated depreciation
Balance, beginning of period	(137,725)	(102,900)	(74,536)
Disposals	39		162
Additions (depreciation and amortization expense)	(42,481)	(34,825)	(28,526)
Balance, end of period	$ (180,167)	$ (137,725)	$ (102,900)

Amount of accumulated depreciation pertaining to real estate investments for entities with a substantial portion of business acquiring and holding investment real estate.

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.FN4)

-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule III)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5

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- Definition

Amount of decrease to accumulated depreciation for real estate investments sold for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

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- Definition

Amount of real estate investments sold for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 205

-SubTopic 10

-Section S99

-Paragraph 6

-Subparagraph (SX 210.5-04.(c) Schedule III)

-URI http://asc.fasb.org/extlink&oid=27047687&loc=d3e5864-122674

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 28

-Article 12

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph c

-Subparagraph Schedule III

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 970

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-28.4)

-URI http://asc.fasb.org/extlink&oid=6590653&loc=d3e638233-123024

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- Definition

Amount, before accumulated depreciation, of real estate investments for entities with a substantial portion of business acquiring and holding investment real estate.

+ References

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- Definition

Amount of increase in real estate investments from acquisitions other than through foreclosure for entities with a substantial portion of business acquiring and holding investment real estate.

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Amount of depreciation expense of real estate investments for entities with a substantial portion of business acquiring and holding investment real estate.

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