Transactions with Affiliates - Schedule of Reinsurance Atlantic States Assumed from Pool (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Ceded Credit Risk [Line Items]
Premiums earned	$ 314,859,014	$ 326,198,234	$ 310,179,267
Liability for losses and loss expenses	470,940,000
Affiliated Entity [Member] | Atlantic States Assumed [Member]
Ceded Credit Risk [Line Items]
Premiums earned	479,835,362	473,512,781	451,470,894
Losses and loss expenses	309,852,141	335,789,280	289,503,373
Unearned premiums	237,106,338	231,958,181	228,988,598
Liability for losses and loss expenses	$ 322,658,731	$ 303,546,744	$ 252,263,547