Note 17 - Earnings Per Share - Basic and Diluted (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share
Net income	$ 13,315,518	$ 8,808,835	$ 10,445,385	$ 10,549,961	$ 9,901,590	$ 7,853,935	$ 8,766,017	$ 9,184,965	$ 43,119,699	$ 35,706,507	$ 27,686,787
Basic earnings per common share (in dollars per share)	$ 0.85	$ 0.56	$ 0.75	$ 0.76	$ 0.72	$ 0.60	$ 0.67	$ 0.70	$ 2.92	$ 2.68	$ 2.20
Diluted earnings per common share (in dollars per share)	$ 0.84	$ 0.55	$ 0.73	$ 0.74	$ 0.70	$ 0.58	$ 0.65	$ 0.68	$ 2.86	$ 2.61	$ 2.17
Weighted average common shares outstanding (in shares)									14,768,687	13,325,128	12,570,767
Weighted average common shares issuable upon exercise of stock options and under the employee stock purchase plan** (in shares)									296,043	355,344	195,236
Weighted average common and common equivalent shares outstanding (in shares)									15,064,730	13,680,472	12,766,003