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