Note 6 - Stock-based Compensation (Details Textual) - $ / shares				1 Months Ended
	Jun. 25, 2018	May 08, 2018	May 07, 2018	May 31, 2012
2012 Stock Incentive Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period				6 years
2012 Stock Incentive Plan [Member] | Stock Options And Stock Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized				4,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				1 year
2012 Stock Incentive Plan [Member] | Stock Options And Stock Appreciation Rights [Member] | Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				2 years
2012 Stock Incentive Plan [Member] | Stock Options And Stock Appreciation Rights [Member] | Share-based Compensation Award, Tranche One [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				100.00%
2012 Stock Incentive Plan [Member] | Stock Options And Stock Appreciation Rights [Member] | Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				3 years
2012 Stock Incentive Plan [Member] | Stock Options And Stock Appreciation Rights [Member] | Share-based Compensation Award, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				50.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				4 years
2012 Stock Incentive Plan [Member] | Stock Options And Stock Appreciation Rights [Member] | Share-based Compensation Award, Tranche Four [Member] | Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage				25.00%
2012 Stock Incentive Plan [Member] | Employee Stock Option [Member] | Non Employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period				1 year
The 2018 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			5,000,000
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period			6 years
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period			10 years
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche One [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		100.00%	100.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche One [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			50.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche One [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		22.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche One [Member] | Employees and Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	50.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Two [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			25.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Two [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		22.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Two [Member] | Employees and Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Three [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage			25.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Three [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		28.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Three [Member] | Employees and Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	25.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights and Restricted Stock Units [Member] | Share-based Compensation Award, Tranche Four [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		28.00%
The 2018 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		295,671
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 14.56
The 2018 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 14.64
The 2018 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	838,117
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 13.82
The 2018 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Director and Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period		5 years 182 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Exercise Price		$ 55.16
The 2018 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		295,671
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 14.57
The 2018 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Employees and Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	6 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 53.44
The 2018 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		40,489
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 54.92
The 2018 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 52.09
The 2018 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	19,848
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 52.03
The 2018 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Director and Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period		5 years 182 days
The 2018 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Chief Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		40,489
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value		$ 54.23
The 2018 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Employees and Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	6 years