Note 7 - Stock-based Compensation - RSU Summary (Details) - $ / shares		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Beginning balance (in shares)		4,144,000	4,270,000	4,232,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share)		$ 39.91	$ 36.47	$ 32.64
Granted (in shares)		1,363,000	666,000	1,349,000
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share)		$ 80.62	$ 66.56	$ 43.28
Vested (in shares)		(853,000)	(772,000)	(975,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share)		$ 44.13	$ 43.39	$ 31.36
Forfeited (in shares)		(21,000)	(20,000)	(336,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share)		$ 76.92	$ 58.46	$ 30.38
Ending balance (in shares)		4,633,000	4,144,000	4,270,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share)		$ 50.94	$ 39.91	$ 36.47
Time-Based RSUs [Member]
Beginning balance (in shares)		258,000	366,000	499,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share)		$ 66.30	$ 51.35	$ 40.75
Granted (in shares)		133,000	81,000	133,000
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share)		$ 114.36	$ 94.25	$ 63
Vested (in shares)		(136,000)	(175,000)	(239,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share)		$ 60.23	$ 48.35	$ 36.43
Forfeited (in shares)		(15,000)	(14,000)	(27,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share)		$ 82.20	$ 61.80	$ 45.35
Ending balance (in shares)		240,000	258,000	366,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share)		$ 95.38	$ 66.30	$ 51.35
PSUs and MPSUs [Member]
Beginning balance (in shares)		2,266,000	2,284,000	1,933,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share)		$ 48.59	$ 43.24	$ 38.99
Granted (in shares)	[1]	630,000	585,000	1,216,000
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share)		$ 85.06	$ 62.72	$ 41.12
Vested (in shares)		(717,000)	(597,000)	(736,000)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share)		$ 41.08	$ 41.94	$ 29.71
Forfeited (in shares)		(5,000)	(6,000)	(129,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share)		$ 63.16	$ 49.82	$ 36.82
Ending balance (in shares)		2,174,000	2,266,000	2,284,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share)		$ 61.61	$ 48.59	$ 43.24
MSUs [Member]
Beginning balance (in shares)		1,620,000	1,620,000	1,800,000
Weighted-Average Grant Date Fair Value Per Share, beginning balance (in dollars per share)		$ 23.57	$ 23.57	$ 23.57
Granted (in shares)		600,000			[1]
Weighted-Average Grant Date Fair Value Per Share, granted (in dollars per share)		$ 68.48
Vested (in shares)
Weighted-Average Grant Date Fair Value Per Share, vested (in dollars per share)
Forfeited (in shares)		(1,000)		(180,000)
Weighted-Average Grant Date Fair Value Per Share, forfeited (in dollars per share)		$ 68.48		$ 23.57
Ending balance (in shares)		2,219,000	1,620,000	1,620,000
Weighted-Average Grant Date Fair Value Per Share, ending balance (in dollars per share)		$ 35.69	$ 23.57	$ 23.57

[1] Amount reflects the number of PSUs and MPSUs that may ultimately be earned based on management's probability assessment of the achievement of performance conditions at each reporting period. In addition, MPSUs are subject to the achievement of market conditions.