Note 5 - Earnings Per Share - Basic and Diluted (Details) - USD ($)		3 Months Ended						9 Months Ended
		Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Net income		$ 6,107,501	$ 6,676,467	$ 6,373,489	$ 6,488,987	$ (523,818)	$ 4,177,889	$ 19,157,457	$ 10,143,058
Basic earnings (loss) per common share (in dollars per share) (in dollars per share)		$ 0.47			$ 0.55			$ 1.55	$ 1.03
Diluted earnings (loss) per common share (in dollars per share) (in dollars per share)		$ 0.46			$ 0.55			$ 1.52	$ 1.01
Weighted average common shares outstanding (in shares)	[1]	13,066,777			11,713,993			12,398,491	9,878,882
Weighted average common shares issuable upon exercise of stock options and under the employee stock purchase plan (in shares)		202,926			161,937			181,551	145,559
Weighted average common and common equivalent shares outstanding (in shares)		13,269,703			11,875,930			12,580,042	10,024,441

[1] The increase in the weighted average common shares outstanding was primarily due to the common stock issuance discussed in Note 9 to the Consolidated Financial Statements.