Condensed Financial Information of Parent Company, Condensed Balance Sheets (Details) - USD ($)	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Assets [Abstract]
Short-term investments	$ 32,305,408	$ 57,321,111
Cash	23,792,273	25,123,332
Property and equipment	2,633,405	2,755,105
Other	451,011	1,123,098
Total assets	2,266,293,888	2,243,349,335
Liabilities [Abstract]
Cash dividends declared to stockholders	5,569,992	5,296,990
Total liabilities	1,786,548,534	1,759,756,323
Stockholders' equity	479,745,354	483,593,012	$ 531,036,087	$ 517,774,120
Total liabilities and stockholders' equity	2,266,293,888	2,243,349,335
Parent Company [Member]
Assets [Abstract]
Investment in subsidiaries/affiliates (equity method)	506,855,000	509,513,000
Short-term investments	1,469,000	7,325,000
Cash	8,043,000	3,288,000	$ 14,375,000	$ 15,321,000
Property and equipment	504,000	586,000
Other	4,866,000	4,589,000
Total assets	521,737,000	525,301,000
Liabilities [Abstract]
Cash dividends declared to stockholders	5,570,000	5,297,000
Notes payable to subsidiary	35,000,000	35,000,000
Other	1,422,000	1,411,000
Total liabilities	41,992,000	41,708,000
Stockholders' equity	479,745,000	483,593,000
Total liabilities and stockholders' equity	$ 521,737,000	$ 525,301,000