Note 15 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]

	2017		2016		2015
Stock options	$	554,435	$	424,904	$	393,114
Restricted stock awards		552,907		460,853		492,410
Stock purchase plan		79,694		61,417		55,945
	$	1,187,036	$	947,174	$	941,469

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

	December 31,
	2017					2016					2015
				Weighted					Weighted					Weighted
				Average					Average					Average
				Exercise					Exercise					Exercise
	Shares			Price		Shares			Price		Shares			Price
Outstanding, beginning		587,961		$	14.83		623,176		$	13.88		661,771		$	13.89
Granted		43,250			43.86		76,749			22.92		73,403			17.63
Exercised		(114,100	)		15.12		(111,423	)		14.97		(79,638	)		14.70
Forfeited		(3,557	)		26.74		(541	)		18.36		(32,360	)		20.69
Outstanding, ending		513,554			17.13		587,961			14.83		623,176			13.88
Exercisable, ending		354,269					385,372					405,832
Weighted average fair value per option granted	$	14.75				$	7.31				$	5.11

Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]

			Options Outstanding
					Weighted				Options Exercisable
					Average		Weighted				Weighted
					Remaining		Average				Average
Range of			Number		Contractual		Exercise		Number		Exercise
Exercise Prices			Outstanding		Life		Price		Exercisable		Price
$7.99	to	$8.93		27,850		3.06	$	8.09		27,850	$	8.09
$9.00	to	$9.30		148,755		2.77		9.22		147,955		9.22
$15.00	to	$16.85		90,668		4.59		15.63		79,369		15.64
$17.10	to	$18.00		132,816		6.57		17.31		81,521		17.26
$21.71	to	$31.53		70,215		8.08		22.63		16,273		22.64
$42.65	to	$48.50		43,250		9.20		43.86		1,301		42.75
				513,554						354,269

Nonvested Restricted Stock Shares Activity [Table Text Block]

	December 31,
	2017			2016			2015
Outstanding, beginning	$	39,438		$	45,046		$	49,833
Granted		28,289			22,382			28,846
Released		(21,338	)		(27,490	)		(33,633	)
Forfeited		-			(500	)		-
Outstanding, ending	$	46,389		$	39,438		$	45,046
Weighted average fair value per share granted	$	44.44		$	22.64		$	17.80

Schedule of Share-based Compensation, Employee Stock Purchase Plan, Activity [Table Text Block]

	2017		2016		2015
Shares granted		12,414		18,711		23,408
Shares purchased		13,318		20,192		24,033
Weighted average fair value per share granted	$	6.42	$	3.28	$	2.39