Note 3 - Stock-based Compensation - RSU Summary (Details) shares in Thousands	9 Months Ended
	Sep. 30, 2019 $ / shares shares
Beginning balance (in shares) | shares	4,633
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 50.94
Granted (in shares) | shares	582
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 101.89
Vested (in shares) | shares	(902)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 48.61
Forfeited (in shares) | shares	(56)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 53.06
Ending balance (in shares) | shares	4,257
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 58.38
Time-Based RSUs [Member]
Beginning balance (in shares) | shares	240
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 95.38
Granted (in shares) | shares	47
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 141.03
Vested (in shares) | shares	(88)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 79.91
Forfeited (in shares) | shares	(6)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 110.23
Ending balance (in shares) | shares	193
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 113.22
PSUs and MPSUs [Member]
Beginning balance (in shares) | shares	2,174
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 61.61
Granted (in shares) | shares	535	[1]
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 98.45
Vested (in shares) | shares	(571)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 54.41
Forfeited (in shares) | shares	(43)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 42.72
Ending balance (in shares) | shares	2,095
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 73.37
MSUs [Member]
Beginning balance (in shares) | shares	2,219
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share) | $ / shares	$ 35.69
Granted (in shares) | shares	0
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 0
Vested (in shares) | shares	(243)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 23.57
Forfeited (in shares) | shares	(7)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 68.48
Ending balance (in shares) | shares	1,969
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 37.08

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