Note 7 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | |
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017 |
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 | | $ 2.9 | | |
Common Class A [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number, Ending Balance | | 0 | | 0 |
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 | | 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 | | $ 12.65 | | |
Service Based Restricted Stock [Member] | Common Class A [Member] | Employee [Member] | Share-based Compensation Award, Tranche One [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | 36,680 | | |
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 | | 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 | | $ 12.65 | | |
Restricted Stock [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 | $ 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 Compensation Award, Tranche One [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | 153,406 | | |
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche Two [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | 82,394 | | |
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche Three [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | | 82,396 | | |
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] | Common Class A [Member] | | | | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period | [1] | 220,080 | 198,220 | |
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value | [1] | $ 12.65 | $ 10.60 | |
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 | |
| |
[1] | For awards subject to future performance conditions, amounts assume target performance. | |