Deferred Policy Acquisition Costs - Changes in Insurance Subsidiaries' Deferred Policy Acquisition Costs (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Insurance [Abstract]
Balance, January 1	$ 60,289,860	$ 56,309,196	$ 52,108,388
Acquisition costs deferred	121,289,267	119,045,664	112,076,808
Amortization charged to earnings	(120,964,000)	(115,065,000)	(107,876,000)
Balance, December 31	$ 60,615,127	$ 60,289,860	$ 56,309,196