Liability for Losses and Loss Expenses - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance [Abstract]
Increase (Decrease) in liability for losses and loss expenses of prior years	$ 6,621,413	$ 2,988,739	$ 7,200,134
Percentage of 2010 development	1.90%	0.90%	2.50%