Financial Highlights - Schedule of Financial Highlights (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
OPERATING PERFORMANCE PER SHARE
Net investment income (usd per share)	$ 0.24	$ 0.28
Net assets at end of period	$ 194,733,622	$ 113,679,482	$ 174,282,891	$ 102,829,810
Investment Company, Dividend Distribution	$ 2,091,351	$ 1,235,971
Class FA
OPERATING PERFORMANCE PER SHARE
Net Asset Value, Beginning of Period (usd per shares)	$ 27.64	$ 26.65
Net investment income, before expense support (usd per shares)	0.20	0.27
Expense support (usd per shares)	0.09	0.04
Net investment income (usd per share)	0.29	0.31
Net realized and unrealized gains (usd per shares)	(0.47)	0.07
Net increase resulting from investment operations (usd per shares)	(0.18)	0.38
Distributions from net investment income (usd per share)	(0.31)	(0.31)
Net Decrease Resulting From Distributions to Shareholders, Per Share (usd per shares)	(0.31)	(0.31)
Net Asset Value, End of Period (usd per shares)	$ 27.15	$ 26.72
Net assets at end of period	$ 126,919,282	$ 89,259,528	117,637,467
Net Assets, Average	$ 124,272,563	$ 87,050,883
Shares outstanding end of period (in shares)	4,674,838.76	3,266,260
Investment Company, Dividend Distribution	$ 1,407,473	$ 1,020,708
Total investment return based on net asset value before total return incentive fee	(0.69%)	1.42%
Ratios to average net assets:
Total operating expenses before expense support	0.47%	0.59%
Net investment income before total return incentive fee(9)	0.15%	0.46%
Net investment income	1.06%	1.15%
Class A
OPERATING PERFORMANCE PER SHARE
Net Asset Value, Beginning of Period (usd per shares)	$ 26.91	$ 26.44
Net investment income, before expense support (usd per shares)	0.07	(0.02)
Expense support (usd per shares)	0.09	0.19
Net investment income (usd per share)	0.16	0.17
Net realized and unrealized gains (usd per shares)	(0.46)	0.09
Net increase resulting from investment operations (usd per shares)	(0.30)	0.26
Distributions from net investment income (usd per share)	(0.31)	(0.31)
Net Decrease Resulting From Distributions to Shareholders, Per Share (usd per shares)	(0.31)	(0.31)
Net Asset Value, End of Period (usd per shares)	$ 26.30	$ 26.39
Net assets at end of period	$ 20,887,589	$ 9,799,809	18,008,048
Net Assets, Average	$ 19,219,301	$ 6,468,700
Shares outstanding end of period (in shares)	794,274.36	371,319
Investment Company, Dividend Distribution	$ 223,612	$ 75,454
Total investment return based on net asset value before total return incentive fee	(1.11%)	1.00%
Ratios to average net assets:
Total operating expenses before expense support	1.01%	2.17%
Net investment income before total return incentive fee(9)	0.67%	1.46%
Net investment income	0.61%	0.63%
Class T
OPERATING PERFORMANCE PER SHARE
Net Asset Value, Beginning of Period (usd per shares)	$ 27.01	$ 26.54
Net investment income, before expense support (usd per shares)	(0.12)	(0.04)
Expense support (usd per shares)	0.16	0.17
Net investment income (usd per share)	0.04	0.13
Net realized and unrealized gains (usd per shares)	(0.44)	0.08
Net increase resulting from investment operations (usd per shares)	(0.40)	0.21
Distributions from net investment income (usd per share)	(0.25)	(0.25)
Net Decrease Resulting From Distributions to Shareholders, Per Share (usd per shares)	(0.25)	(0.25)
Net Asset Value, End of Period (usd per shares)	$ 26.36	$ 26.50
Net assets at end of period	$ 8,813,664	$ 1,477,301	5,366,259
Net Assets, Average	$ 6,597,543	$ 1,072,524
Shares outstanding end of period (in shares)	334,314.61	55,739
Investment Company, Dividend Distribution	$ 60,942	$ 10,024
Total investment return based on net asset value before total return incentive fee	(1.49%)	0.79%
Ratios to average net assets:
Total operating expenses before expense support	1.89%	2.13%
Net investment income before total return incentive fee(9)	1.28%	1.50%
Net investment income	0.16%	0.48%
Class D
OPERATING PERFORMANCE PER SHARE
Net Asset Value, Beginning of Period (usd per shares)	$ 26.61	$ 26.23
Net investment income, before expense support (usd per shares)	0.08	0.15
Expense support (usd per shares)	0.00	0.00
Net investment income (usd per share)	0.08	0.15
Net realized and unrealized gains (usd per shares)	(0.47)	0.07
Net increase resulting from investment operations (usd per shares)	(0.39)	0.22
Distributions from net investment income (usd per share)	(0.28)	(0.28)
Net Decrease Resulting From Distributions to Shareholders, Per Share (usd per shares)	(0.28)	(0.28)
Net Asset Value, End of Period (usd per shares)	$ 25.94	$ 26.17
Net assets at end of period	$ 8,624,930	$ 3,607,349	8,053,103
Net Assets, Average	$ 8,292,032	$ 3,387,992
Shares outstanding end of period (in shares)	332,537.51	137,864
Investment Company, Dividend Distribution	$ 88,027	$ 36,428
Total investment return based on net asset value before total return incentive fee	(1.47%)	0.85%
Ratios to average net assets:
Total operating expenses before expense support	0.98%	1.12%
Net investment income before total return incentive fee(9)	0.98%	1.12%
Net investment income	0.29%	0.58%
Class I
OPERATING PERFORMANCE PER SHARE
Net Asset Value, Beginning of Period (usd per shares)	$ 27.15	$ 26.55
Net investment income, before expense support (usd per shares)	0.08	0.05
Expense support (usd per shares)	0.10	0.17
Net investment income (usd per share)	0.18	0.22
Net realized and unrealized gains (usd per shares)	(0.47)	0.08
Net increase resulting from investment operations (usd per shares)	(0.29)	0.30
Distributions from net investment income (usd per share)	(0.31)	(0.31)
Net Decrease Resulting From Distributions to Shareholders, Per Share (usd per shares)	(0.31)	(0.31)
Net Asset Value, End of Period (usd per shares)	$ 26.55	$ 26.54
Net assets at end of period	$ 29,242,887	$ 11,535,495	25,218,014
Net Assets, Average	$ 27,011,432	$ 8,027,629
Shares outstanding end of period (in shares)	1,101,367.19	434,646
Investment Company, Dividend Distribution	$ 311,297	$ 93,357
Total investment return based on net asset value before total return incentive fee	(1.07%)	1.15%
Ratios to average net assets:
Total operating expenses before expense support	0.98%	1.80%
Net investment income before total return incentive fee(9)	0.60%	1.18%
Net investment income	0.67%	0.83%
Common Class S- [Member]
OPERATING PERFORMANCE PER SHARE
Net Asset Value, Beginning of Period (usd per shares)	$ 27.56
Net investment income, before expense support (usd per shares)	(0.39)
Expense support (usd per shares)	0.39
Net investment income (usd per share)	0.00
Net realized and unrealized gains (usd per shares)	(0.40)
Net increase resulting from investment operations (usd per shares)	(0.40)
Distributions from net investment income (usd per share)	(0.00)
Net Decrease Resulting From Distributions to Shareholders, Per Share (usd per shares)	(0.00)
Net Asset Value, End of Period (usd per shares)	$ 27.16
Net assets at end of period	$ 245,270		$ 0
Net Assets, Average	$ 245,270
Shares outstanding end of period (in shares)	9,030.21
Investment Company, Dividend Distribution	$ 0
Total investment return based on net asset value before total return incentive fee	(1.45%)
Ratios to average net assets:
Total operating expenses before expense support	1.91%
Net investment income before total return incentive fee(9)	0.46%
Net investment income	0.00%