Note 8 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended |
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount, Total | $ 11 | | |
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition | 1 year 7 months 6 days | | |
Restricted Stock [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 751,463 | 391,836 | 307,943 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 16.07 | $ 14.63 | $ 10.40 |
Restricted Stock [Member] | Employee [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | 318,196 | 307,943 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | | $ 15.25 | |
Restricted Stock [Member] | Employee [Member] | Share-based Payment Arrangement, Tranche One [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 11,223 | 131,106 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 17.83 | | |
Restricted Stock [Member] | Employee [Member] | Share-based Payment Arrangement, Tranche Two [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 32,680 | 69,651 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 15.92 | | |
Restricted Stock [Member] | Employee [Member] | Share-based Payment Arrangement, Tranche Three [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | 69,652 | |
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche One, Vesting January 31, 2018 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 102,648 |
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche Two, Vesting January 31, 2019 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 102,648 |
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche Three, Vesting January 31, 2020 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 102,647 |
Restricted Stock [Member] | Certain Employees One [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 340,993 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 14.85 | | |
Restricted Stock [Member] | Certain Employees Two [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 277,048 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 16.55 | | |
Restricted Stock [Member] | Certain Employees Two [Member] | Share-based Payment Arrangement, Tranche One [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 92,349 | | |
Restricted Stock [Member] | Certain Employees Two [Member] | Share-based Payment Arrangement, Tranche Two [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 92,350 | | |
Restricted Stock [Member] | Nonemployee Directors [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 41,181 | 73,640 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 22.10 | | |
Restricted Stock [Member] | Director [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 76,856 |
Restricted Stock [Member] | Common Class A [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 199,810 | 220,080 | 275,076 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 15.36 | $ 12.65 | $ 10.84 |
Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 198,220 |
Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | Share-based Compensation Award, Tranche One, Vesting January 31, 2018 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 66,073 |
Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | Share-based Compensation Award, Tranche Two, Vesting January 31, 2019 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 66,073 |
Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | Share-based Compensation Award, Tranche Three, Vesting January 31, 2020 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 66,074 |
Service Based Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 99,905 | 110,040 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 15.36 | $ 12.65 | |
Service Based Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | Share-based Payment Arrangement, Tranche One [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 33,302 | 36,680 | |
Service Based Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | Share-based Payment Arrangement, Tranche Two [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 33,301 | 36,680 | |
Performance Based Restricted Stock [Member] | Employee [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 48,338 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 16.55 | | |
Performance Based Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 99,905 | 110,040 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 15.36 | $ 12.65 | |
Restricted Stock Units (RSUs) [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 398,000 | 0 | 215,500 |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | $ 18.21 | $ 0 | $ 15.70 |
Restricted Stock Units (RSUs) [Member] | Share-based Compensation Award, Tranche One, Vesting January 31, 2018 [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | | 209,500 |
Directors Restricted Stock Plan [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award Maximum Number of Restricted Shares Authorized Yearly Per Director | 10,000 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 770,000 | | |
Directors Restricted Stock Plan [Member] | Restricted Stock [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | 0 | 0 | 0 |
The 2017 Equity and Incentive Compensation Plan [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 3,700,000 | | |
The 2017 Equity and Incentive Compensation Plan [Member] | Common Class A [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 1,500,000 | | |
2007 Incentive Plan [Member] | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant | 0 | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance | 274,746 | 274,746 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance | $ 1.99 | $ 1.99 | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | $ 5 | | |