Investment In and Advances to Affiliate - Schedule of Revenue From Contracts With Customers Included in Fee and Other Income on Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	$ 14,394	$ 6,499	$ 28,437	$ 23,051
Retail Value Inc. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	8,900		8,900
Asset and Property Management Fees [Member]
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	10,501	4,660	20,982	16,851
Asset and Property Management Fees [Member] | Retail Value Inc. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	6,500		6,500
Leasing Commissions [Member]
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	1,818	1,521	4,752	4,849
Leasing Commissions [Member] | Retail Value Inc. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	700		700
Disposition Fees [Member]
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	1,622	$ 0	1,622	$ 0
Disposition Fees [Member] | Retail Value Inc. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	1,600		1,600
Guaranty Fee [Member] | Retail Value Inc. [Member]
Disaggregation Of Revenue [Line Items]
Total revenue from contracts with customers	$ 100		$ 100