Reinsurance - Ceded Reinsurance Transactions with Unaffiliated Reinsurers (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Ceded Credit Risk [Line Items]
Premiums written	$ 320,956,412	$ 293,379,217	$ 269,363,012
Premiums earned	310,179,267	282,646,219	271,712,289
Prepaid reinsurance premiums	135,032,641	124,255,495
Unaffiliated Entity [Member]
Ceded Credit Risk [Line Items]
Premiums written	51,241,267	45,354,233	40,997,351
Premiums earned	49,633,348	44,318,542	49,758,371
Losses and loss expenses	44,575,268	18,588,114	30,722,807
Prepaid reinsurance premiums	11,213,665	9,605,746	8,570,055
Liability for losses and loss expenses	$ 116,689,871	$ 103,694,418	$ 113,023,942