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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income—diluted		$ 142,797	$ 65,142	$ 466,232	$ 114,057
Dilutive effect of share-based compensation arrangements	[1]	4,593	4,096	4,284	4,027
Adjusted average common shares outstanding—diluted		217,902	219,391	218,783	220,230
Net income (loss) per share—diluted		$ 0.66	$ 0.30	$ 2.13	$ 0.52
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income—basic		$ 142,797	$ 65,142	$ 466,232	$ 114,272
Average common shares outstanding - basic		213,309	215,279	214,499	215,194
Net income (loss) per share - basic		$ 0.67	$ 0.30	$ 2.17	$ 0.53
Convertible Debt | Convertible Senior Notes Due 2019
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Adjustment for dilutive Convertible Senior Notes due 2019, net of tax	[2]	$ 0	$ 0	$ 0	$ (215)
Dilutive effect of Convertible Senior Notes		0	0	0	611
Convertible Debt | Convertible Senior Notes Due 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Dilutive effect of Convertible Senior Notes		0	16	0	398
Stock Compensation Plan [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares of common stock equivalents		338	676	338	440

[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 (loss) per share because they were anti-dilutive:   Three Months Ended
September 30,   Nine Months Ended
September 30, (In thousands) 2018   2017   2018   2017 Shares of common stock equivalents 338
  676
  338
  440

[2] As applicable, includes coupon interest, amortization of discount and fees, and other changes in income that would result from the assumed conversion. Included in the nine months ended September 30, 2017 is a benefit related to our adjustment of estimated accrued expense to actual amounts, resulting from the January 2017 settlement of our obligations on the remaining Convertible Senior Notes due 2019.