Reinsurance - Total Ceded Reinsurance Transactions with both Affiliated and Unaffiliated Reinsurers (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Ceded Credit Risk [Line Items]
Premiums earned	$ 310,179,267	$ 282,646,219	$ 271,712,289
Prepaid reinsurance premiums	135,032,641	124,255,495
Affiliated Entity and Unaffiliated Entity [Member]
Ceded Credit Risk [Line Items]
Premiums earned	310,179,267	282,646,219	271,712,289
Losses and loss expenses	218,523,260	156,479,885	172,302,366
Prepaid reinsurance premiums	135,032,641	124,255,495	113,522,505
Liability for losses and loss expenses	$ 293,271,257	$ 259,147,147	$ 256,150,860