Note 15 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Notes Tables

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

	2018		2017		2016
Stock options	$	471,849	$	554,435	$	424,904
Restricted stock awards		856,731		552,907		460,853
Stock purchase plan		114,766		79,694		61,417
	$	1,443,346	$	1,187,036	$	947,174

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

	December 31,
	2018				2017				2016
			Weighted				Weighted				Weighted
			Average				Average				Average
			Exercise				Exercise				Exercise
	Shares		Price		Shares		Price		Shares		Price
Outstanding, beginning		513,554	$	17.13		587,961	$	14.83		623,176	$	13.88
Granted		16,315		44.02		43,250		43.86		76,749		22.92
Exercised		(60,127)		13.56		(114,100)		15.12		(111,423)		14.97
Forfeited		(170)		16.81		(3,557)		26.74		(541)		18.36
Outstanding, ending		469,572		18.52		513,554		17.13		587,961		14.83
Exercisable, ending		358,270				354,269				385,372
Weighted average fair value per option granted	$	14.68			$	14.75			$	7.31

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	24,175	2.07	$	8.10	24,175	$	8.10
$9.00 to $9.30	121,724	2.10		9.21	121,724		9.21
$15.08 to $16.13	74,703	4.24		15.63	72,303		15.64
$17.10 to $18.00	125,137	5.56		17.31	99,573		17.29
$21.71 to $31.53	66,291	7.11		22.92	29,633		22.64
$42.65 to $48.50	57,542	8.46		43.94	10,862		43.79
	469,572				358,270

Nonvested Restricted Stock Shares Activity [Table Text Block]

	December 31,
	2018		2017		2016
Outstanding, beginning		46,389		39,438		45,046
Granted*		37,315		28,289		22,382
Released		(19,605)		(21,338)		(27,490)
Forfeited		—		—		(500)
Outstanding, ending		64,099		46,389		39,438
Weighted average fair value per share granted	$	43.50	$	44.44	$	22.64

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

	2018		2017		2016
Shares granted		17,305		12,414		18,711
Shares purchased		15,528		13,318		20,192
Weighted average fair value per share granted	$	6.63	$	6.42	$	3.28