Note 7 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | |
Mar. 31, 2020 | Mar. 31, 2019 | Dec. 31, 2019 |
2007 Incentive Plan [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance (in shares) | | 0 | | 274,746 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price, Ending Balance (in dollars per share) | | | | $ 1.99 |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value | | $ 3 | | |
Service Based Restricted Stock [Member] | Employee [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 207,787 | | |
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) | | $ 21.69 | | |
Service Based 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 (in shares) | | 69,262 | | |
Service Based 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 (in shares) | | 69,263 | | |
Service Based 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 (in shares) | | 69,262 | | |
Service Based Restricted Stock [Member] | Employee [Member] | Common Class A [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 83,407 | 99,905 | |
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) | | $ 19.87 | $ 15.36 | |
Service Based Restricted Stock [Member] | Employee [Member] | Common Class A [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 (in shares) | | 27,802 | 33,302 | |
Service Based Restricted Stock [Member] | Employee [Member] | Common Class A [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 (in shares) | | 27,803 | 33,301 | |
Service Based Restricted Stock [Member] | Employee [Member] | Common Class A [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 (in shares) | | 27,802 | 33,302 | |
Performance Based Restricted Stock [Member] | Employee [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 40,756 | 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 (in dollars per share) | | $ 21.69 | $ 16.55 | |
Performance Based Restricted Stock [Member] | Employee [Member] | Common Class A [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 83,407 | 99,905 | |
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) | | $ 19.87 | $ 15.36 | |
Restricted Stock Units (RSUs) [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 90,184 | 0 | |
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) | | $ 18.92 | $ 0 | |
Restricted Stock Units (RSUs) [Member] | Employee [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | 90,184 | | |
Restricted Stock Units (RSUs) [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 (in shares) | | 60,052 | | |
Restricted Stock Units (RSUs) [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 (in shares) | | 15,066 | | |
Restricted Stock Units (RSUs) [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 (in shares) | | 15,066 | | |
Restricted Stock [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | [1] | 248,543 | 677,602 | |
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) | [1] | $ 21.69 | $ 15.72 | |
Restricted Stock [Member] | Common Class A [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | [1] | 166,814 | 199,810 | |
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) | [1] | $ 19.87 | $ 15.36 | |
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 (in shares) | | | 11,223 | |
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) | | | $ 17.83 | |
Restricted Stock [Member] | Certain Employees One [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period (in shares) | | | 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 (in dollars per share) | | | $ 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 (in shares) | | | 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 (in dollars per share) | | | $ 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 (in shares) | | | 92,349 | |
Restricted Stock [Member] | Certain Employees Two [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 (in shares) | | | 92,350 | |
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 (in shares) | | | 92,349 | |
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[1] | For awards subject to future performance conditions, amounts assume target performance. | |