Income Taxes - Provision for Income Tax (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of Income Tax Expense (Benefit), Continuing Operations [Abstract]
Current	$ (2,139,061)	$ 8,496,405	$ 5,621,367
Deferred	7,137,423	2,030,865	980,868
Federal income tax provision	$ 4,998,362	$ 10,527,270	$ 6,602,235