Note 2 - Net Earnings Per Common Share - Earnings Per Common Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019	Mar. 31, 2018
Stockholders	$ 2,547,000	$ (2,715,000)	$ (1,321,000)	$ 2,829,000	$ 1,559,000	$ (672,000)	$ 422,000	$ 968,000	$ 1,339,995	$ 2,277,109
Basic (in dollars per share)	$ 1.25	$ (1.34)	$ (0.65)	$ 1.38	$ 0.76	$ (0.33)	$ 0.21	$ 0.47	$ 0.66	$ 1.11
Diluted (in dollars per share)	$ 1.25	$ (1.34)	$ (0.65)	$ 1.38	$ 0.76	$ (0.33)	$ 0.21	$ 0.47	$ 0.66	$ 1.11
Basic (in shares)									2,034,749	2,042,806
Diluted (in shares)									2,039,892	2,047,685