Investments in Real Estate - Narrative (Detail) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Real Estate Properties [Line Items]
Cost of construction in progress	$ 187.1	$ 127.0
Metropolis Dr., Austin, TX (Austin 4)
Real Estate Properties [Line Items]
Purchase price	17.3
Metropolis Dr., Austin, TX (Austin 1)
Real Estate Properties [Line Items]
Impairment related to exit	9.2
Land \| Metropolis Dr., Austin, TX (Austin 4)
Real Estate Properties [Line Items]
Purchase price	$ 3.3

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.

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 210.12-28.4)

-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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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration