Note 14 - Equity-based Compensation - Stock Appreciation Rights (Details) - Stock Appreciation Rights (SARs) [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Outstanding, stock appreciation rights (in shares)	90,605	102,458	136,000
Outstanding, weighted average exercise price (in dollars per share)	$ 550.60	$ 477.62	$ 426.80
Outstanding, beginning balance, weighted average fair value (in dollars per share)	$ 153.90	$ 122.29	$ 100.91	$ 88.07
Outstanding, aggregate intrinsic value	$ 73,419	$ 24,673	$ 23,173	$ 26,510
Weighted average remaining contractual term, outstanding (Year)	7 years 6 months	7 years 2 months 12 days	8 years 1 month 6 days	8 years 8 months 12 days
Granted, stock appreciation rights (in shares)	29,000	21,000	24,432
Granted, weighted average exercise price (in dollars per share)	$ 900.90	$ 744.47	$ 632.15
Granted, weighted average fair value (in dollars per share)	$ 209.57	$ 181.21	$ 140.44
Weighted average remaining contractual term, granted (Year)	8 years 9 months 18 days	8 years 8 months 12 days	9 years 1 month 6 days
Exercised, stock appreciation rights (in shares)	(26,092)	(27,060)	(41,603)
Exercised, weighted average exercise price (in dollars per share)	$ 491.12	$ 435.11	$ 424.02
Exercised, weighted average fair value (in dollars per share)	$ 105.94	$ 90.06	$ 87.54
Exercised, aggregate intrinsic value	$ 20,143	$ 9,418	$ 11,596
Forfeited, stock appreciation rights (in shares)	(3,103)	(5,793)	(16,371)
Forfeited, weighted average exercise price (in dollars per share)	$ 659.01	$ 502.08	$ 422.31
Forfeited, weighted average fair value (in dollars per share)	$ 154.49	$ 108.22	$ 87.22
Outstanding, stock appreciation rights (in shares)	90,410	90,605	102,458	136,000
Outstanding, weighted average exercise price (in dollars per share)	$ 676.41	$ 550.60	$ 477.62	$ 426.80
Vested and exercisable, stock appreciation rights (in shares)	35,393
Vested and exercisable, weighted average exercise price (in dollars per share)	$ 489.11
Vested and exercisable, weighted average fair value (in dollars per share)	$ 104.63
Vested and exercisable, aggregate intrinsic value	$ 35,370
Weighted average remaining contractual term, vested and exercisable (Year)	6 years 1 month 6 days