Note 2 - Net Income Per Share Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)—diluted		$ 173,438	$ 142,797	$ 511,125	$ 466,232
Dilutive effect of share-based compensation arrangements	[1]	5,584	4,593	5,402	4,284
Adjusted average common shares outstanding—diluted		208,691	217,902	213,963	218,783
Net income (loss) per share—diluted		$ 0.83	$ 0.66	$ 2.39	$ 2.13
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) - basic		$ 173,438	$ 142,797	$ 511,125	$ 466,232
Average common shares outstanding - basic		203,107	213,309	208,561	214,499
Net income (loss) per share - basic		$ 0.85	$ 0.67	$ 2.45	$ 2.17
Stock Compensation Plan
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Shares of common stock equivalents		0	338	160	338

[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
September 30,   Nine Months Ended
September 30, (In thousands) 2019   2018   2019   2018 Shares of common stock equivalents —
  338
  160
  338