Transactions with Affiliates - Schedule of Reinsurance Atlantic States Ceded to Pool (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Ceded Credit Risk [Line Items]
Premiums earned	$ 326,198,234	$ 310,179,267	$ 282,646,219
Prepaid reinsurance premiums	135,379,777	135,032,641
Affiliated Entity [Member] | Atlantic States Ceded [Member]
Ceded Credit Risk [Line Items]
Premiums earned	212,928,238	200,752,599	185,444,009
Losses and loss expenses	159,495,489	140,015,950	115,371,839
Prepaid reinsurance premiums	106,224,424	103,991,861	95,469,329
Liability for losses and loss expenses	$ 158,081,925	$ 136,786,070	$ 120,434,535