Note 6 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	274,746		274,746
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 1.99		$ 1.99
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 3.4
Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	0		0
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	307,943	237,500
Restricted Stock [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	198,220	218,612
Restricted Stock [Member] | Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	307,943	218,452
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	198,220	166,677
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 One, Vesting January 31, 2018 [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	66,073
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] | Employee [Member] | Share-based Compensation Award, Tranche Three, Vesting January 31, 2020 [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	66,074
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche One, Vesting January 31, 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		72,816
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche One, Vesting January 31, 2017 [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		55,559
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche Two, Vesting January 31, 2018 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		72,816
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche Two, Vesting January 31, 2018 [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		55,559
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche Three, Vesting January 31, 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		72,820
Restricted Stock [Member] | Employee [Member] | Share-based Compensation Award, Tranche Three, Vesting January 31, 2019 [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		55,559
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 Two, Vesting January 31, 2019 [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	66,073
Restricted Stock [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		19,048
Restricted Stock [Member] | Director [Member] | Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		51,935