Financial Highlights - Schedule of Financial Highlights (Parenthetical) (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Mar. 31, 2017
Schedule Of Financial Highlights [Line Items]
Weighted average units outstanding	35,541,295	21,194,302
Net assets value per unit	$ 8.466	$ 8.469
Total return based on net asset value	7.37%	9.13%
Ratio of net investment income to average net assets	7.42%	8.52%
Ratio of net operating expenses to average net assets	3.58%	2.17%
Class C and Class I Units [Member]
Schedule Of Financial Highlights [Line Items]
Distribution and dealer manager fees payable	$ 1,895,000
Class A Units [Member]
Schedule Of Financial Highlights [Line Items]
Net assets value per unit	$ 8.466	$ 8.534	$ 8.507	$ 8.529
Class C Units [Member]
Schedule Of Financial Highlights [Line Items]
Net assets value per unit	8.466	8.534	8.507	8.267
Class I Units [Member]
Schedule Of Financial Highlights [Line Items]
Net assets value per unit	8.466	8.534	8.507	$ 8.529
Class Y Units [Member]
Schedule Of Financial Highlights [Line Items]
Net assets value per unit	$ 8.466	$ 8.534	$ 8.507
Responsibility Agreement [Member]
Schedule Of Financial Highlights [Line Items]
Total return based on net asset value	6.09%	6.18%
Ratio of net investment income to average net assets	6.14%	5.77%
Ratio of net operating expenses to average net assets	4.86%	4.92%