Note 8 - Stock-based Compensation - RSU Summary (Details) - $ / shares		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Balance (in shares)		3,105,000	4,053,000	4,633,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share)		$ 87.42	$ 59.16	$ 50.94
Granted (in shares)		411,000	703,000	564,000
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share)		$ 357.49	$ 175.12	$ 103.68
Vested (in shares)		(972,000)	(1,623,000)	(1,083,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share)		$ 72.69	$ 54.70	$ 47.34
Forfeited (in shares)		(35,000)	(28,000)	(61,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share)		$ 124.50	$ 96.35	$ 57.01
Balance (in shares)		2,509,000	3,105,000	4,053,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share)		$ 136.87	$ 87.42	$ 59.16
Time-Based RSUs [Member]
Balance (in shares)		161,000	180,000	240,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share)		$ 151.62	$ 115.45	$ 95.38
Granted (in shares)		46,000	76,000	52,000
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share)		$ 384.33	$ 189.28	$ 141.32
Vested (in shares)		(71,000)	(86,000)	(103,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share)		$ 144.46	$ 110.67	$ 81.53
Forfeited (in shares)		(11,000)	(9,000)	(9,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share)		$ 207.04	$ 138.34	$ 117.31
Balance (in shares)		125,000	161,000	180,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share)		$ 235.82	$ 151.62	$ 115.45
PSUs and MPSUs [Member]
Balance (in shares)		1,390,000	1,987,000	2,174,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share)		$ 132.60	$ 74.50	$ 61.61
Granted (in shares)	[1]	365,000	627,000	512,000
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share)		$ 354.12	$ 173.40	$ 99.88
Vested (in shares)		(577,000)	(1,213,000)	(656,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share)		$ 91.50	$ 59.03	$ 53.72
Forfeited (in shares)		(12,000)	(11,000)	(43,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share)		$ 103.84	$ 84.48	$ 42.72
Balance (in shares)		1,166,000	1,390,000	1,987,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share)		$ 222.78	$ 132.60	$ 74.50
MSUs [Member]
Balance (in shares)		1,554,000	1,886,000	2,219,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share)		$ 40.40	$ 37.63	$ 35.69
Granted (in shares)		0	0	0
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share)		$ 0	$ 0	$ 0
Vested (in shares)		(324,000)	(324,000)	(324,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share)		$ 23.57	$ 23.57	$ 23.57
Forfeited (in shares)		(12,000)	(8,000)	(9,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share)		$ 68.48	$ 68.48	$ 68.48
Balance (in shares)		1,218,000	1,554,000	1,886,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share)		$ 44.59	$ 40.40	$ 37.63

[1] Amount reflects the number of awards that may ultimately be earned based on management’s probability assessment of the achievement of performance conditions at each reporting period.