Note 1 - Summary of Significant Accounting Policies - Fair Value of Financial Assets and Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Total carrying amount of long-term debt	$ 37,079	$ 37,966
Estimated fair value of long-term debt	37,619	38,257
Fair Value, Recurring [Member]
Assets, fair value	1,443	1,848
Money Market Funds [Member] | Fair Value, Recurring [Member]
Assets, fair value	1,443	1,848
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Assets, fair value	1,443	1,848
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member] | Fair Value, Recurring [Member]
Assets, fair value	1,443	1,848
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Assets, fair value
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member] | Fair Value, Recurring [Member]
Assets, fair value
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Assets, fair value
Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member] | Fair Value, Recurring [Member]
Assets, fair value