Related Party Transactions and Arrangements - Additional Information (Detail) - USD ($)			1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 30, 2020	Jul. 31, 2020	Mar. 31, 2017	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Winthrop Advisor and its Affiliates [Member]
Related Party Transaction [Line Items]
Fees paid to related parties				$ 300,000	$ 317,000	$ 900,000	$ 1,017,000
Liquidation Value [Member] | Asset Management Fees [Member]
Related Party Transaction [Line Items]
Fees paid to related parties	$ 83,000
Liquidation Value [Member] | Advisor [Member] | Post Liquidation Date Agreement Monthly Supplemental Fee [Member]
Related Party Transaction [Line Items]
Fees paid to related parties		$ 100,000
Liquidation Value [Member] | Advisor [Member] | Post Liquidation Date Agreement Quarterly Supplemental Fee [Member]
Related Party Transaction [Line Items]
Fees paid to related parties		$ 50,000
Liquidation Value [Member] | Service Provider and Affiliates [Member]
Related Party Transaction [Line Items]
Incentive fee, percentage of excess of hurdle amount			10.00%
Hurdle amount (in dollars per share)			$ 110.00
Liquidation Value [Member] | Winthrop Advisor and its Affiliates [Member] | Asset Management Fees [Member]
Related Party Transaction [Line Items]
Asset management fees				$ 1,200,000		$ 1,200,000		$ 1,200,000