Note 7 - Stock-based Awards (Details Textual) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands						12 Months Ended
	Dec. 16, 2020	Nov. 11, 2020	May 03, 2019	Jul. 24, 2018	May 03, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2006	Jan. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross (in shares)		40				40
Share Price (in dollars per share)		$ 1.13	$ 2.99	$ 5.49	$ 5.69	$ 5.09	$ 9.15
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)				21.04		$ 3.47	$ 3.40	$ 2.49
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value						$ 274	$ 223	$ 308
Conversion of Stock, Amount Issued						$ 115	$ 144	$ 493
Stock Unit Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)	5	190				195
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)						$ 4.89	$ 12.01	$ 14.42
Stock Unit Award [Member] | Share-based Payment Arrangement, Nonemployee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	2 years
Stock Unit Award [Member] | Share-based Payment Arrangement, Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	4 years
Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)	10 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in dollars per share)		$ 4.07	$ 10.60	$ 19.83
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term (Year)				6 years 91 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate		45.00%	41.00%	39.00%	38.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate		0.90%	2.40%	3.40%	3.40%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate		4.00%	3.90%	4.10%	4.20%
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total						$ 1,100
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition (Year)						3 years 36 days
Share-based Payment Arrangement, Option [Member] | Share-based Payment Arrangement, Nonemployee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	2 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)						2 years
Minimum [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term (Year)		5 years 273 days	5 years 273 days		5 years 273 days
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)						4 years
Maximum [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term (Year)		6 years 91 days	6 years 91 days		6 years 91 days
Maximum [Member] | Share-based Payment Arrangement, Option [Member] | Share-based Payment Arrangement, Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period (Year)	4 years
Incentive Plan 2006 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period (Year)									10 years
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)						45			850	1,200
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares)						0
Common Stock, Capital Shares Reserved for Future Issuance (in shares)						815