Note 2 - Net Income Per Share Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income—diluted		$ 166,730	$ 208,949	$ 337,687	$ 323,435
Dilutive effect of share-based compensation arrangements	[1]	5,506	3,854	5,236	3,692
Adjusted average common shares outstanding—diluted		213,603	217,830	216,500	218,741
Net income (loss) per share—diluted		$ 0.78	$ 0.96	$ 1.56	$ 1.48
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income - basic		$ 166,730	$ 208,949	$ 337,687	$ 323,435
Average common shares outstanding - basic		208,097	213,976	211,264	215,049
Net income (loss) per share - basic		$ 0.80	$ 0.98	$ 1.60	$ 1.50
Stock Compensation Plan
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares of common stock equivalents		168	484	168	351

[1] The following number of shares of our common stock equivalents issued under our share-based compensation arrangements were not included in the calculation of diluted net income per share because they were anti-dilutive:   Three Months Ended
June 30,   Six Months Ended
June 30, (In thousands) 2019   2018   2019   2018 Shares of common stock equivalents 168
  484
  168
  351