Note 3 - Stock-based Compensation - RSU Summary (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Beginning balance (in shares) | shares	4,053,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 59.16
Granted (in shares) | shares	371,000
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 170.56
Vested (in shares) | shares	(1,084,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 54.85
Forfeited (in shares) | shares	(12,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 83.20
Ending balance (in shares) | shares	3,328,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 72.88
Time-Based RSUs [Member]
Beginning balance (in shares) | shares	180,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 115.45
Granted (in shares) | shares	47,000
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 183.53
Vested (in shares) | shares	(24,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 104.06
Forfeited (in shares) | shares	(2,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 114.71
Ending balance (in shares) | shares	201,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 132.71
PSUs and MPSUs [Member]
Beginning balance (in shares) | shares	1,987,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 74.50
Granted (in shares) | shares	324,000	[1]
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 168.69
Vested (in shares) | shares	(979,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 56.22
Forfeited (in shares) | shares	(7,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 81.64
Ending balance (in shares) | shares	1,325,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 110.99
MSUs [Member]
Beginning balance (in shares) | shares	1,886,000
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	(81,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 23.57
Forfeited (in shares) | shares	(3,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 68.48
Ending balance (in shares) | shares	1,802,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 38.21

[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.