Organization and Basis of Presentation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Organization And Basis Of Presentation [Abstract]
Month and year of incorporation	2007-01
Cash and cash equivalents	$ 7,679,267	$ 9,007,071	$ 8,691,155