Note 12 - Information about Stock Options Outstanding (Details)	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Exercise Price Range One [Member]
Range of exercise prices, lower limit (in dollars per share)	$ 0
Range of exercise prices, upper limit (in dollars per share)	$ 7.85
Options outstanding (in shares) | shares	59,441
Options outstanding, weighted average remaining contractual life	2 years 277 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 5.03
Options exercisable (in shares) | shares	59,441
Options exercisable, weighted average exercise price (in dollars per share)	$ 5.03
Exercise Price Range Two [Member]
Options outstanding (in shares) | shares	206,955
Options outstanding, weighted average remaining contractual life	4 years 357 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 7.86
Options exercisable (in shares) | shares	206,955
Options exercisable, weighted average exercise price (in dollars per share)	$ 7.86
Exercise price (in dollars per share)	7.86
Exercise Price Range Three [Member]
Range of exercise prices, lower limit (in dollars per share)	7.87
Range of exercise prices, upper limit (in dollars per share)	$ 31.43
Options outstanding (in shares) | shares	138,831
Options outstanding, weighted average remaining contractual life	6 years 54 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 28.19
Options exercisable (in shares) | shares	72,495
Options exercisable, weighted average exercise price (in dollars per share)	$ 27.22
Exercise Price Range Four [Member]
Range of exercise prices, lower limit (in dollars per share)	31.44
Range of exercise prices, upper limit (in dollars per share)	$ 47.15
Options outstanding (in shares) | shares	88,146
Options outstanding, weighted average remaining contractual life	7 years 36 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 45.14
Options exercisable (in shares) | shares	19,504
Options exercisable, weighted average exercise price (in dollars per share)	$ 42.70
Exercise Price Range Five [Member]
Range of exercise prices, lower limit (in dollars per share)	47.16
Range of exercise prices, upper limit (in dollars per share)	$ 66.87
Options outstanding (in shares) | shares	96,474
Options outstanding, weighted average remaining contractual life	7 years 317 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 57.52
Options exercisable (in shares) | shares	36,934
Options exercisable, weighted average exercise price (in dollars per share)	$ 55.87
Exercise Price Range Six [Member]
Range of exercise prices, lower limit (in dollars per share)	66.88
Range of exercise prices, upper limit (in dollars per share)	$ 78.59
Options outstanding (in shares) | shares	176,195
Options outstanding, weighted average remaining contractual life	8 years 273 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 71.54
Options exercisable (in shares) | shares	13,972
Options exercisable, weighted average exercise price (in dollars per share)	$ 78.53
Options outstanding (in shares) | shares	766,042
Options outstanding, weighted average exercise price (in dollars per share)	$ 36.52