Financial Highlights - Schedule of Financial Highlights (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Net asset value at beginning of period			$ 8.47	$ 8.54
Net investment income	$ 0.18	$ 0.20	0.49	0.56
Net change in unrealized depreciation on investments				0.00
Net increase in net assets resulting from operations			0.49	0.56
Net change in offering costs			0.03	(0.02)
Distributions			(0.54)	(0.56)
Net change in accrued distribution and other fees			0.01	(0.07)
Net decrease in net assets			(0.02)	(0.08)
Net asset value at end of period	$ 8.45	$ 8.46	$ 8.45	$ 8.46
Total return based on net asset value			5.74%	6.50%
Net assets at end of period	$ 312,070,024	$ 223,109,319	$ 312,070,024	$ 223,109,319	$ 250,755,915	$ 138,620,607
Units Outstanding at end of period	36,914,426	26,372,641	36,914,426	26,372,641	29,607,381
Ratio/Supplemental data (annualized):
Ratio of net investment income to average net assets			7.70%	8.51%
Ratio of net operating expenses to average net assets			2.96%	2.27%