Note 15 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Share-based Compensation, Stock Options, Activity [Table Text Block]

	Number of options			Weighted average exercise price	Weighted average remaining contractual life (years)		Aggregate intrinsic value
Shares issuable under options - December 31, 2012	1,729,200		$	22.31
Granted	422,000			31.35
Exercised	(464,150	)		16.20
Shares issuable under options - December 31, 2013	1,687,050		$	26.25
Granted	343,000			49.57
Exercised	(558,150	)		19.26
Forfeited	(8,000	)		31.28
Shares issuable under options - December 31, 2014	1,463,900		$	34.35
Granted	698,500			36.61
Exercised	(699,400	)		20.09
Forfeited	(22,500	)		38.71
Shares issuable under options - December 31, 2015	1,440,500		$	28.65	3.2	$	22,900
Options exercisable - End of year	241,150		$	22.55	1.9	$	5,305

Stock Options Exercised [Table Text Block]

		2015		2014		2013
Number of options exercised		699,400		558,150		464,150
Aggregate fair value	$	35,516	$	27,973	$	16,780
Intrinsic value		21,463		17,223		9,313
Amount of cash received		14,053		10,750		7,467
Tax benefit recognized	$	91	$	5,856	$	3,148

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

		2015			2014			2013
Risk free rate		1.0	%		0.9	%		0.4	%
Expected life in years		4.75			4.75			4.75
Expected volatility		28.6	%		25.5	%		37.5	%
Dividend yield		0.2	%		0.8	%		0.0	%
Weighted average fair value per option granted	$	11.91		$	10.52		$	10.13