Note 5 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jan. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	[1]			8 years 36 days		8 years 73 days
Incentive Plan 2006 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant		221		221		77	350
Share-based Payment Arrangement, Expense, Tax Benefit		$ 0	$ 0	$ 0	$ 0
Share Price		$ 9.11		$ 9.11
Common Stock, Capital Shares Reserved for Future Issuance		835		835
Share-based Payment Arrangement, Nonvested Award, Option, Cost Not yet Recognized, Amount		$ 1,400		$ 1,400
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term				2 years 328 days

[1] The aggregate intrinsic value on this table was calculated based on the amount, if any, by which the closing market value of the Company's stock on September 30, 2019 ($9.11) exceeded the exercise price of the underlying options, multiplied by the number of shares subject to each option.