Segment Reporting - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Investments in real estate, Book Value	$ 1,840,451	$ 1,131,931	$ 1,015,581
IRT
Segment Reporting Information [Line Items]
Investments in real estate, Book Value	$ 689,112	$ 190,096

Amount of real estate investment property 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.

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

Name:	us-gaap_RealEstateInvestmentPropertyAtCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant