Note 15 - Stock-based Compensation (Details Textual) - USD ($) $ / shares in Units, $ in Millions											1 Months Ended	12 Months Ended
		Nov. 07, 2018	Jun. 25, 2018	May 08, 2018	May 07, 2018	Nov. 08, 2017	Aug. 04, 2017	Jun. 07, 2017	Nov. 08, 2016	Jun. 13, 2016	May 31, 2012	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Total												$ 17.0
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition												1 year 109 days
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Annual Forfeiture Rate												5.30%	1.10%	10.30%
Increase (Decrease) In Stock Based Compensation Expense Due To Forfeitures, Percent												381.80%	(89.30%)	7.00%
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions Dividends Growth Rate												20.00%
Sharebased Compensation Arrangement By Sharebased Payment Award Fair Value Assumptions Weighted Average Expected Dividend Rate												0.90%
Share Price												$ 52.30	$ 63.96
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number												846,215	431,387
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value												$ 5.2	$ 38.9
Weighted Average [Member]
Share Price												$ 55.58	$ 58.82
Stock Appreciation Rights (SARs) [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value												14.80
Stock Appreciation Rights (SARs) [Member] | Employees [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
Restricted Stock Units (RSUs) [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value												$ 52.60
SARs and RSUs [Member] | Vesting After the Second Year from the Grant Date [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		50.00%
SARs and RSUs [Member] | Vesting After the Third and Forth Year from the Grant Date [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		25.00%
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] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period											10 years
2012 Stock Incentive Plan [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross							30,000
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price							$ 57.97
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] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period							1 year
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period							7 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value							$ 18.42
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
2012 Stock Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period										4 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period								5 years		6 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period								23,200		1,080,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Exercise Price								$ 58.79		$ 42.87
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value								$ 13.67
2012 Stock Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period									1 year
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period									7 years
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period									60,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Exercise Price									$ 47.46
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value									$ 14.51
2012 Stock 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										11.98
2012 Stock Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Other Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value										$ 11.42
2012 Stock Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Directors and Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period						108,771
2012 Stock Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage								50.00%		50.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period										2 years
2012 Stock Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage								25.00%		25.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period										3 years
2012 Stock Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member] | Share-based Compensation Award, Tranche Three [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										4 years
2012 Stock Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Directors and Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period						22,742
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Exercise Price						$ 63.35
2012 Stock Incentive Plan [Member] | SARs and RSUs [Member] | Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage						100.00%
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period						6 years
The 2018 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized					5,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant												3,605,740
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] | 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] | 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]
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period		6 years
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			841,117
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, 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] | Stock Appreciation Rights (SARs) [Member] | Directors and Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		35,395
Share-based Compensation Arrangements by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Exercise Price		$ 53.16
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
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, Weighted Average Grant Date Fair Value				$ 54.23
The 2018 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Directors and Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period		13,688
The 2018 Incentive Plan [Member] | SARs and RSUs [Member] | Vesting After the First Year from the Grant Date [Member] | Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage		100.00%
2012 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross													30,000	1,155,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value													$ 57.97	$ 43.01
2012 Incentive Plan [Member] | Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	[1]											1,172,000	132,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	[1]											$ 53.87	$ 62.55
2012 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, Weighted Average Grant Date Fair Value						$ 17.60
2012 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						17.70
2012 Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	[2]											74,000	23,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	[2]
2012 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, Weighted Average Grant Date Fair Value						62.90
2012 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						$ 62.30
2012 Incentive Plan [Member] | SARs and RSUs [Member] | Vesting Each Year [Member] | Senior Management [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage						25.00%
The 2012 and 2004 Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant												0

[1] Upon exercise, SARs entitle the recipient to receive shares of common stock equal to the increase in value of the award between the grant date and the exercise date.

[2] An RSU represents the right to receive one share of common stock once certain vesting conditions are met. The value of an RSU is identical to the value of the underlying stock.