Note 3 - Stock-based Compensation - RSU Summary (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2020 $ / shares shares
Beginning balance (in shares) | shares	4,053
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 59.16
Granted (in shares) | shares	453
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 171.47
Vested (in shares) | shares	(1,280)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 55.30
Forfeited (in shares) | shares	(18)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 89.81
Ending balance (in shares) | shares	3,208
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 76.39
Time-Based RSUs [Member]
Beginning balance (in shares) | shares	180
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 115.45
Granted (in shares) | shares	70
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 181.41
Vested (in shares) | shares	(60)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 105.95
Forfeited (in shares) | shares	(4)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 129.31
Ending balance (in shares) | shares	186
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 143.09
PSUs and MPSUs [Member]
Beginning balance (in shares) | shares	1,987
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 74.50
Granted (in shares) | shares	383	[1]
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 169.65
Vested (in shares) | shares	(1,058)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 57.29
Forfeited (in shares) | shares	(9)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 83.15
Ending balance (in shares) | shares	1,303
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 116.39
MSUs [Member]
Beginning balance (in shares) | shares	1,886
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 37.63
Granted (in shares) | shares	0
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 0
Vested (in shares) | shares	(162)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 23.57
Forfeited (in shares) | shares	(5)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 68.48
Ending balance (in shares) | shares	1,719
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 38.86

[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.