Securities - Amortized Cost and Estimated Fair Value of Securities Available-for-Sale (Detail) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 485,362,359	$ 516,006,296
Gross Unrealized Gains	84,772	1,101,494
Gross Unrealized Losses	21,694,946	12,061,413
Estimated Fair Value	463,752,185	505,046,377
Obligations of U.S. Government Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	99,566,635	180,647,580
Gross Unrealized Losses	4,269,911	4,199,022
Estimated Fair Value	95,296,724	176,448,558
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	278,584,218	213,707,125
Gross Unrealized Gains	6,438	43,197
Gross Unrealized Losses	12,561,575	5,327,265
Estimated Fair Value	266,029,081	208,423,057
State, County and Municipal [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	107,211,506	118,786,297
Gross Unrealized Gains	78,334	849,364
Gross Unrealized Losses	4,863,460	2,535,126
Estimated Fair Value	$ 102,426,380	117,100,535
Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,865,294
Gross Unrealized Gains		208,933
Estimated Fair Value		$ 3,074,227