Summary of Significant Accounting Policies - Summary of the Calculation of Basic and Diluted EPS (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accounting Policies [Abstract]
Net loss/ net decrease in net assets resulting from operations available to common shareholders	$ (14,647)	$ (4,797)	$ (29,521)	$ (3,686)
Weighted average common shares outstanding applicable to basic EPS	24,230,815	23,925,567	24,193,057	23,909,344
Effect of dilutive stock options	0	0	0	0
Effect of restricted stock grants	0	0	0	0
Adjusted weighted average common shares outstanding applicable to diluted EPS	24,230,815	23,925,567	24,193,057	23,909,344
Basic earnings per share	$ (0.60)	$ (0.20)	$ (1.22)	$ (0.15)
Diluted loss per share	$ (0.60)	$ (0.20)	$ (1.22)	$ (0.15)