Real Estate Properties under Development, Net - Additional Information (Detail) - Buildings - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Real Estate [Line Items]
Scheduled minimum rental payments to be received		$ 1,897
Lease expiration date	Oct. 31, 2017

Future minimum rental payments in aggregate as of the balance sheet date under operating leases.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164653&loc=d3e41551-112718

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