Note 2 - Summary of Significant Accounting Policies (Details Textual) - USD ($)	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2019	Dec. 31, 2018	Feb. 23, 2018
Accounts Receivable, Allowance for Credit Loss, Current	$ 139,000			$ 139,000			$ 139,000
Accounts Receivable, Credit Loss Expense (Reversal)	3,000			3,000	$ 33,000
Inventory Write-down	0			0
Deferred Rent Credit	15,000			15,000			64,000
Asset Impairment Charges, Total			$ 0	$ 127,000	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options and Warrants, Outstanding, Number	2,203,499		2,662,766	2,203,499	2,662,766
Share-based Compensation Arrangement by Share-based Payment Award, Options and Warrants, Outstanding, Aggregate Intrinsic Value	$ 103,000			$ 103,000
Payments of Dividends, Total				0
Operating Lease, Liability, Total	4,902,000			4,902,000		$ 2,400,000
Operating Lease, Right-of-Use Asset	$ 4,899,000			$ 4,899,000		2,400,000
Accounting Standards Update 2016-02 [Member]
Operating Lease, Liability, Total						2,400,000
Operating Lease, Right-of-Use Asset						$ 2,400,000
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member]
Open Tax Year				2015 2016 2017 2018
State and Local Jurisdiction [Member]
Open Tax Year				2014 2015 2016 2017 2018
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative, Notional Amount								$ 10,000,000
Derivative, Fixed Interest Rate								2.52%
Disposal Wells [Member]
Asset Impairment Charges, Total		$ 127,000
Minimum [Member]
Property, Plant and Equipment, Useful Life				5 years
Maximum [Member]
Property, Plant and Equipment, Useful Life				30 years