Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

Reference 1: 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 2: 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

Reference 3: 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

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

Real Estate Investments - Purchase Price Allocation (Parenthetical) (Details) - USD ($) $ in Thousands	Jan. 05, 2018	Mar. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Outstanding principal balance on mortgage debt assumed		$ 325,974	$ 317,216
Four Tower Bridge [Member] \| Intangible Assets Acquired [Member]
Business Acquisition [Line Items]
Weighted average amortization period	4 years 1 month 6 days
Four Tower Bridge [Member] \| Below Market Lease [Member]
Business Acquisition [Line Items]
Weighted average amortization period	4 years 9 months 18 days
Four Tower Bridge [Member] \| Mortgage Debt Assumed - at Fair Value [Member]
Business Acquisition [Line Items]
Outstanding principal balance on mortgage debt assumed	$ 9,700