Note 3 - Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) - basic	$ 135,103	$ 173,438	$ 245,613	$ 511,125
Average common shares outstanding - basic	193,176	203,107	196,120	208,561
Net income (loss) per share - basic	$ 0.70	$ 0.85	$ 1.25	$ 2.45
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income (loss)—diluted	$ 135,103	$ 173,438	$ 245,613	$ 511,125
Dilutive effect of share-based compensation arrangements	980	5,584	1,127	5,402
Adjusted average common shares outstanding—diluted	194,156	208,691	197,247	213,963
Net income (loss) per share—diluted	$ 0.70	$ 0.83	$ 1.25	$ 2.39
Stock Compensation Plan
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Shares of common stock equivalents	710	0	1,046	160