Note 15 - Stock Based Compensation - Stock Options Outstanding by Range of Exercise Prices (Details)	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Range of exercise prices, minimum (in dollars per share)	$ 17.55
Range of exercise prices, maximum (in dollars per share)	$ 48.13
Options outstanding, number of shares (in shares) | shares	430,820
Options outstanding, weighted average remaining contractual life (Year)	7 years 43 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 43.82
Options exercisable, number of shares (in shares) | shares	324,622
Options exercisable, weighted average exercise price (in dollars per share)	$ 43.23
Range01 [Member]
Range of exercise prices, minimum (in dollars per share)	17.55
Range of exercise prices, maximum (in dollars per share)	$ 21.13
Options outstanding, number of shares (in shares) | shares	3,950
Options outstanding, weighted average remaining contractual life (Year)	2 years 277 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 19.38
Options exercisable, number of shares (in shares) | shares	3,950
Options exercisable, weighted average exercise price (in dollars per share)	$ 19.38
Range 02 [Member]
Range of exercise prices, minimum (in dollars per share)	21.29
Range of exercise prices, maximum (in dollars per share)	$ 21.29
Options outstanding, number of shares (in shares) | shares	3,700
Options outstanding, weighted average remaining contractual life (Year)	5 years 109 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 21.29
Options exercisable, number of shares (in shares) | shares	2,500
Options exercisable, weighted average exercise price (in dollars per share)	$ 21.29
Range 03 [Member]
Range of exercise prices, minimum (in dollars per share)	21.51
Range of exercise prices, maximum (in dollars per share)	$ 21.51
Options outstanding, number of shares (in shares) | shares	1,250
Options outstanding, weighted average remaining contractual life (Year)	2 years 109 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 21.51
Options exercisable, number of shares (in shares) | shares	1,250
Options exercisable, weighted average exercise price (in dollars per share)	$ 21.51
Range 04 [Member]
Range of exercise prices, minimum (in dollars per share)	30.31
Range of exercise prices, maximum (in dollars per share)	$ 30.31
Options outstanding, number of shares (in shares) | shares	22,180
Options outstanding, weighted average remaining contractual life (Year)	229 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 30.31
Options exercisable, number of shares (in shares) | shares	22,180
Options exercisable, weighted average exercise price (in dollars per share)	$ 30.31
Range 05 [Member]
Range of exercise prices, minimum (in dollars per share)	40.57
Range of exercise prices, maximum (in dollars per share)	$ 40.57
Options outstanding, number of shares (in shares) | shares	40,490
Options outstanding, weighted average remaining contractual life (Year)	7 years 91 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 40.57
Options exercisable, number of shares (in shares) | shares	40,490
Options exercisable, weighted average exercise price (in dollars per share)	$ 40.57
Range 06 [Member]
Range of exercise prices, minimum (in dollars per share)	40.72
Range of exercise prices, maximum (in dollars per share)	$ 40.72
Options outstanding, number of shares (in shares) | shares	1,500
Options outstanding, weighted average remaining contractual life (Year)	7 years 47 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 40.72
Options exercisable, number of shares (in shares) | shares	600
Options exercisable, weighted average exercise price (in dollars per share)	$ 40.72
Range 07 [Member]
Range of exercise prices, minimum (in dollars per share)	44.40
Range of exercise prices, maximum (in dollars per share)	$ 44.40
Options outstanding, number of shares (in shares) | shares	49,870
Options outstanding, weighted average remaining contractual life (Year)	7 years 91 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 44.40
Options exercisable, number of shares (in shares) | shares	37,144
Options exercisable, weighted average exercise price (in dollars per share)	$ 44.40
Range 08 [Member]
Range of exercise prices, minimum (in dollars per share)	45.50
Range of exercise prices, maximum (in dollars per share)	$ 45.50
Options outstanding, number of shares (in shares) | shares	246,485
Options outstanding, weighted average remaining contractual life (Year)	7 years 226 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 45.50
Options exercisable, number of shares (in shares) | shares	193,025
Options exercisable, weighted average exercise price (in dollars per share)	$ 45.50
Range 09 [Member]
Range of exercise prices, minimum (in dollars per share)	47.02
Range of exercise prices, maximum (in dollars per share)	$ 47.02
Options outstanding, number of shares (in shares) | shares	58,090
Options outstanding, weighted average remaining contractual life (Year)	7 years 288 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 47.02
Options exercisable, number of shares (in shares) | shares	20,838
Options exercisable, weighted average exercise price (in dollars per share)	$ 47.02
Range 10 [Member]
Range of exercise prices, minimum (in dollars per share)	48.13
Range of exercise prices, maximum (in dollars per share)	$ 48.13
Options outstanding, number of shares (in shares) | shares	3,305
Options outstanding, weighted average remaining contractual life (Year)	7 years 350 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 48.13
Options exercisable, number of shares (in shares) | shares	2,645
Options exercisable, weighted average exercise price (in dollars per share)	$ 48.13