Note 7 - Equity Plans (Details Textual) - USD ($) | Mar. 13, 2017 | Jul. 01, 2016 | May 01, 2016 | Mar. 31, 2017 | Sep. 30, 2016 | Jun. 30, 2016 | Dec. 31, 2016 | Dec. 31, 2015 |
Senior Management Compensation Program [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Minimum Number of Shares Per Employee | | | | | | 750 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Matching Purchase Requirement | | | | | | 500 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Match | | | | | | 250 | | |
Restricted Stock Units (RSUs) [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | | 50,033 | | | | |
Restricted Stock Units (RSUs) [Member] | Senior Management Stock Incentive Program [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | | 5 years | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Participant's Base Salary | | 10.00% | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Amount Per Employee | | $ 17,500 | | | | | | |
Restricted Stock Units (RSUs) [Member] | Senior Management Compensation Program [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Plan Modification, Remaining Liability Reversed | | | | | | | $ 1,000,000 | |
Restricted Stock Units (RSUs) [Member] | Senior Management Compensation Program [Member] | Five Year Anniversary [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | | | | | | $ 25,000 | | |
Restricted Stock Units (RSUs) [Member] | Senior Management Compensation Program [Member] | Ten Year Anniversary [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | | | | | | 50,000 | | |
Restricted Stock Units (RSUs) [Member] | Senior Management Compensation Program [Member] | Fifteen Year Anniversary [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | | | | | | 75,000 | | |
Restricted Stock Units (RSUs) [Member] | Senior Management Compensation Program [Member] | Twenty Five Year Anniversary [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | | | | | | 100,000 | | |
Restricted Stock Units (RSUs) [Member] | Senior Management Compensation Program [Member] | Twenty Year Anniversary [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Vested | | | | | | $ 100,000 | | |
Restricted Stock Units (RSUs) [Member] | Non-Employee Director [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 3,501 | | 3,094 | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period | | | | 1 year | | | | |
Restricted Stock Units (RSUs) [Member] | Executive Vice President and Chief Operating Officer [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | | | 10,573 | | | |
Match [Member] | Senior Management Compensation Program [Member] | | | | | | | | |
Shares Matched | | | | | | 2,500 | | 9,000 |
Common Stock [Member] | | | | | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | | | | 1,000,000 | | | | |
Share Price | $ 19.99 | | $ 22.62 | | | | | |