Selected Financial Ratios and Other Data - Summary of Selected Financial Ratios and Other Data (Detail) - USD ($)		3 Months Ended		6 Months Ended
		Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2018	Dec. 31, 2017
Net share data
Net asset value at the beginning of the period		$ 11,800	$ 11,910	$ 11,910
Net investment loss		(0.15)	(0.14)	(0.19)
Income tax benefit		0.03	0.29	0.37
Net realized gains (losses) on investments		(1.44)	0.08	0.12
Net change in unrealized appreciation (depreciation) on investments		0.94	(0.43)	(0.45)
Net decrease in net assets resulting from operations		(0.62)	(0.20)	(0.15)
Issuance of common stock		(0.03)	0.06	(0.11)
Repurchase of common stock		$ 0	$ 0	$ 0
Net investment income		$ 0	$ 0	$ 0
Return of capital		$ 0	$ 0	$ 0
Net realized gains on investments		0	0	0
Total distributions		0	0	0
Other		0	0	0
Total decrease in net asset value		(0.65)	(0.26)	(0.26)
Net asset value at the end of the period	[1]	11,150	11,650	11,650
Per share market value at beginning of period		3.53	1.98	3.02
Per share market value at end of period		$ 4.65	$ 2.39	$ 2.39
Total return	[2]	129.00%	83.00%	(42.00%)
Ratios/supplemental data
Total shareholders' equity (net assets)		$ 272,437,000	$ 282,739,000	$ 282,739,000	$ 284,916,000	$ 287,159,000
Average net assets		$ 284,021,000	$ 287,153,000	$ 286,123,000
Total expense ratio	[3],[4]	10.02%	0.10%	2.58%
Operating expenses to average net assets	[3]	5.87%	5.14%	4.16%
Net investment income after income taxes to average net assets	[3]	(4.61%)	(1.81%)	(1.22%)

[1] Includes $0 and $0 of undistributed net investment income per share and $0 and $0 of undistributed net realized gains per share as of March 31, 2018 and June 30, 2017.

[2] Total return is calculated by dividing the change in market value of a share of common stock during the period, assuming the reinvestment of distributions on the payment date, by the per share market value at the beginning of the period.

[3] MSC has assumed certain of the Company's servicing obligations, and as a result, servicing fee income of $1,290 and $1,295, and operating expenses of $1,150 and $925, which formerly were the Company's were now MSC's for the three months ended March 31, 2018 and June 30, 2017 and were $2,608 of servicing fee income, and $2,092 of operating expenses for the six months ended June 30, 2017. Excluding the impact of the MSC amounts, the total expense ratio, operating expense ratio, and net investment income ratio would have been 11.75%, 6.88%, and 7.51% in the March 31, 2018 quarter, 1.66%, 6.44%, and (1.56%) in the June 30, 2017 quarter, and 4.25%, 5.64%, and (1.22%) in the six months ended June 30, 2017.

[4] Total expense ratio represents total expenses (interest expense, operating expenses, and income taxes) divided by average net assets.