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, 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
Weighted average number of common shares outstanding - basic (in shares)									3,388,624	3,346,689	3,283,177
Effect of dilutive securities (in shares)									46,238	98,943	121,519
Weighted average number of common shares and potential common shares - diluted (in shares)									3,434,862	3,445,632	3,404,696
Net income									$ 9,467	$ 12,115	$ 5,146
Net income per common share - basic (in dollars per share)	$ 0.66	$ 0.69	$ 0.86	$ 0.59	$ 2.21	$ 0.67	$ 0.46	$ 0.48	$ 2.79	$ 3.62	$ 1.57
Net income per common share - diluted (in dollars per share)	$ 0.65	$ 0.67	$ 0.85	$ 0.58	$ 2.14	$ 0.65	$ 0.45	$ 0.47	$ 2.76	$ 3.52	$ 1.51