Note 12 - Equity Compensation Plans - Summary of Stock Activity (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
		Mar. 31, 2022	Dec. 31, 2021
Outstanding beginning balance, options (in shares)		5,067,098
Outstanding beginning balance, options, weighted average exercise price (in dollars per share)		$ 115.73
Outstanding, options, aggregate intrinsic value		$ 572.6
Granted, options (in shares)		608,598
Granted, options, weighted average exercise price (in dollars per share)		$ 198.15
Dividend reinvestment, options (in shares)		0
Dividend reinvestment, options, weighted average exercise price (in (in dollars per share)		$ 0
Exercised or lapsed, options (in shares)		(164,742)
Exercised or lapsed, options, weighted average exercise price (in dollars per share)		$ 100.50
Exercised or lapsed, options, aggregate intrinsic value		$ 16.2
Canceled, expired or forfeited, option (in shares)		(35,641)
Canceled, expired or forfeited, options, weighted average exercise price (in dollars per share)		$ 166.26
Outstanding, option (in shares)		5,475,313
Outstanding beginning balance, options, weighted average exercise price (in dollars per share)		$ 124.11
Outstanding, options, aggregate intrinsic value		$ 495.6
Exercisable, options (in shares)		3,448,475	3,173,592
Exercisable, options, weighted average exercise price (in dollars per share)		$ 99.55	$ 89.14
Exercisable, options, aggregate intrinsic value		$ 396.9	$ 443.0
Nonvested, options (in shares)		2,026,838
Expected to vest, options (in shares)		1,748,384
Restricted Stock [Member]
Outstanding beginning balance, number of shares (in shares)		351,504
Outstanding beginning balance, weighted average exercise price (in dollars per share)		$ 161.33
Granted, number of shares (in shares)		147,218
Granted, weighted average exercise price (in dollars per share)		$ 196.02
Dividend reinvestment, number of shares (in shares)		0
Dividend reinvestment (in dollars per share)		$ 0
Exercised or lapsed, number of shares (in shares)		(74,494)
Exercised or lapsed, weighted average exercise price (in dollars per share)		$ 174.22
Canceled, expired or forfeited, number of shares (in shares)		(6,464)
Canceled, expired or forfeited, weighted average exercise price (in dollars per share)		$ 166.22
Outstanding ending balance, number of shares (in shares)		417,764
Outstanding ending balance, weighted average exercise price (in dollars per share)		$ 171.18
Nonvested, number of shares (in shares)		417,764	351,504
Expected, number of shares (in shares)		363,686
Performance Shares [Member]
Outstanding beginning balance, number of shares (in shares)		163,123
Outstanding beginning balance, weighted average exercise price (in dollars per share)		$ 192.99
Granted, number of shares (in shares)		74,887
Granted, weighted average exercise price (in dollars per share)		$ 201.27
Dividend reinvestment, number of shares (in shares)		302
Exercised or lapsed, number of shares (in shares)		(52,256)
Exercised or lapsed, weighted average exercise price (in dollars per share)		$ 173.59
Canceled, expired or forfeited, number of shares (in shares)		0
Outstanding ending balance, number of shares (in shares)		186,056
Outstanding ending balance, weighted average exercise price (in dollars per share)		$ 201.78
Nonvested, number of shares (in shares)		186,056	163,123
Expected, number of shares (in shares)	[1]	88,916

[1] Includes estimated performance achievement