Stock Transactions and Unit Redemptions - Unit Redemption and Share Repurchase Activity (Detail) - USD ($)	1 Months Ended			3 Months Ended		6 Months Ended
	Jun. 30, 2018	May 01, 2018	Apr. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018
Stock Transactions Parenthetical Disclosures [Abstract]
Redemptions, Number of Units				4,299,936	1,723,654	6,023,590
Repurchases, Number of Shares	6,543	281,339	438,657			726,539
Total Redemptions and Repurchases						6,750,129
Redemptions, Average Price Paid per Unit				$ 13.10	$ 14.34	$ 13.45
Redemptions, Average Price Paid per Unit	$ 11.65	$ 13.12	$ 13.55			13.37
Total Redemptions and Repurchases						$ 13.44
Total Redemptions and Repurchases, Approximate Dollar Value of Units and Shares That May Yet Be Redeemed/Purchased Under the Plan	$ 106,137,021			$ 106,137,021		$ 106,137,021