Variable Interest Entities - Additional Information (Detail) $ in Thousands	9 Months Ended
Sep. 30, 2017 USD ($) Property Venture	Dec. 31, 2016 USD ($)
Variable Interest Entity [Line Items]
Number of industrial properties \| Property	2
Number of joint venture \| Venture	2
Total investment in mortgages and loans, net	$ 1,235,206	$ 1,280,285
Indebtedness	1,427,947	1,751,082
VIE
Variable Interest Entity [Line Items]
Total investment in mortgages and loans, net	984,356	1,184,588
Indebtedness	962,324	1,288,258
VIE \| Consolidation Eliminations
Variable Interest Entity [Line Items]
Total investment in mortgages and loans, net	426,887	549,879
Indebtedness	$ 437,546	$ 510,244

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_LongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant