Liability for Losses and Loss Expenses - Summary of Insurance Subsidiaries' Liability for Losses and Loss Expenses (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Liability for Claims and Claims Adjustment Expense [Abstract]
Balance at January 1	$ 814,665,224	$ 676,671,727	$ 606,664,590
Less reinsurance recoverable	(339,267,525)	(293,271,257)	(259,147,147)
Net balance at January 1	475,397,699	383,400,470	347,517,443
Incurred related to:
Current year	519,319,941	540,826,810	480,646,641
Prior years	(12,932,277)	35,631,610	6,621,413
Total incurred	506,387,664	576,458,420	487,268,054
Paid related to:
Current year	278,923,614	308,578,285	288,379,600
Prior years	195,956,327	175,882,906	163,005,427
Total paid	474,879,941	484,461,191	451,385,027
Net balance at end of period	506,905,422	475,397,699	383,400,470
Plus reinsurance recoverable	362,768,427	339,267,525	293,271,257
Balance at end of period	$ 869,673,849	$ 814,665,224	$ 676,671,727