Note 15 - Stock-based Compensation - Summary of Options Outstanding (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options outstanding, shares (in shares)	1,163,381	1,239,407	177,959
Options outstanding, weighted average exercise price (in dollars per share)	$ 71.16	$ 71.19	$ 55.48
Options granted, shares (in shares)	53,316	110,265	1,125,443
Options granted, weighted average exercise price (in dollars per share)	$ 77.89	$ 61.39	$ 72.96
Options exercised, shares (in shares)	(346,168)	(68,291)	(48,995)
Options exercised, weighted average exercise price (in dollars per share)	$ 71.57	$ 54.31	$ 51.25
Options cancelled, shares (in shares)	(85,000)	(118,000)	(15,000)
Options cancelled, weighted average exercise price (in dollars per share)	$ 72.94	$ 72.11	$ 72.94
Options outstanding, shares (in shares)	785,529	1,163,381	1,239,407
Options outstanding, weighted average exercise price (in dollars per share)	$ 71.24	$ 71.16	$ 71.19
Options outstanding, aggregate intrinsic value	$ 11,931,000
Options exercisable, shares (in shares)	204,029
Options exercisable, weighted average exercise price (in dollars per share)	$ 68.20
Options exercisable, aggregate intrinsic value	$ 3,720,000