Disposition of Real Estate and Discontinued Operations - Additional Information (Detail) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2015 USD ($) Property	Dec. 31, 2014 Property
Discontinued Operations And Disposal Groups [Abstract]
Number of properties sold	22
Proceeds from sale of real estate \| $	$ 297.3
Number of properties sold under discontinued operations		35

Cash received from the sale of real estate that is held for investment, that is, it is part of an investing activity during the period.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3179-108585

Name:	us-gaap_ProceedsFromSaleOfRealEstateHeldforinvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration