Condensed Financial Information of Parent Company, Condensed Balance Sheets (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assets [Abstract]
Short-term investments	$ 12,692,341	$ 20,900,155
Cash	57,709,375	103,094,236
Property and equipment	2,956,930	4,390,377
Other	1,612,732	1,393,053
Total assets	2,255,175,399	2,160,520,324
Liabilities [Abstract]
Cash dividends declared to stockholders	4,915,268	4,436,301
Other	7,557,757	6,470,652
Total liabilities	1,724,139,312	1,642,746,204
Stockholders' equity	531,036,087	517,774,120	$ 451,015,519	$ 398,869,901
Total liabilities and stockholders' equity	2,255,175,399	2,160,520,324
Parent Company [Member]
Assets [Abstract]
Investment in subsidiaries/affiliates (equity method)	554,804,000	540,665,000
Short-term investments	9,000	9,000
Cash	14,375,000	15,321,000	$ 2,350,000	$ 1,542,000
Property and equipment	716,000	833,000
Other	2,455,000	1,721,000
Total assets	572,359,000	558,549,000
Liabilities [Abstract]
Cash dividends declared to stockholders	4,915,000	4,436,000
Notes payable to subsidiary	35,000,000	35,000,000
Other	1,408,000	1,339,000
Total liabilities	41,323,000	40,775,000
Stockholders' equity	531,036,000	517,774,000
Total liabilities and stockholders' equity	$ 572,359,000	$ 558,549,000