Note 10 - Net Income Per Common Share - Reconciliation of Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Weighted average number of common shares outstanding - basic (in shares)									3,412,805	3,388,624	3,346,689
Effect of dilutive securities (in shares)									17,648	46,238	98,943
Weighted average number of common shares and potential common shares - diluted (in shares)									3,430,453	3,434,862	3,445,632
Net income									$ 7,796	$ 9,467	$ 12,115
Net income per common share - basic (in dollars per share)	$ 0.58	$ 0.53	$ 0.50	$ 0.67	$ 0.66	$ 0.69	$ 0.86	$ 0.59	$ 2.28	$ 2.79	$ 3.62
Net income per common share - diluted (in dollars per share)	$ 0.58	$ 0.53	$ 0.50	$ 0.66	$ 0.65	$ 0.67	$ 0.85	$ 0.58	$ 2.27	$ 2.76	$ 3.52