Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value Option Quantitative Disclosures [Line Items]
Transfers between Level 1, 2 and 3 in fair value measurement hierarchy	$ 0	$ 0	$ 0	$ 0
Unfunded Commitments	8,632,000		8,632,000		$ 10,300,000
EGCP III [Member]
Fair Value Option Quantitative Disclosures [Line Items]
Unfunded Commitments	$ 7,847,000		$ 7,847,000
End of the investment period			Oct. 12, 2016
Remaining obligation date			Oct. 12, 2023