Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Option Quantitative Disclosures [Line Items]
Transfers between Level 1, 2 and 3 in fair value measurement hierarchy	$ 0	$ 0
Unfunded Commitments	10,300,000	$ 9,183,000
EGCP III [Member]
Fair Value Option Quantitative Disclosures [Line Items]
Unfunded Commitments	$ 8,613,000
End of the investment period	Oct. 12, 2016
Remaining obligation date	Oct. 12, 2023