Note 3 - Stock-based Compensation - RSU Summary (Details) shares in Thousands	6 Months Ended
	Jun. 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	484	[1]
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 106.41
Vested (in shares) | shares	(715)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 50.52
Forfeited (in shares) | shares	(8)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 87.85
Ending balance (in shares) | shares	4,394
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 57.05
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	44	[1]
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 140.59
Vested (in shares) | shares	(68)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 80.27
Forfeited (in shares) | shares	(4)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 106.51
Ending balance (in shares) | shares	212
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 109.33
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	440	[1]
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share) | $ / shares	$ 103.02
Vested (in shares) | shares	(485)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share) | $ / shares	$ 55.36
Forfeited (in shares) | shares	0
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 0
Ending balance (in shares) | shares	2,129
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 71.60
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	[1]
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	(4)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share) | $ / shares	$ 68.48
Ending balance (in shares) | shares	2,053
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share) | $ / shares	$ 36.58

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