Note 2 - Net Income Per Share Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net Income (Loss) Available to Common Stockholders, Diluted		$ 65,142	$ 83,651	$ 114,057	$ 252,315
Dilutive effect of share-based compensation arrangements (2)	[1]	4,096	3,129	4,027	2,846
Adjusted average common shares outstanding—diluted		219,391	225,968	220,230	230,672
Net income (loss)—diluted		$ 0.30	$ 0.37	$ 0.52	$ 1.09
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income—basic		$ 65,142	$ 82,803	$ 114,272	$ 247,164
Average common shares outstanding - basic		215,279	214,387	215,194	210,858
Net income per share - basic		$ 0.30	$ 0.39	$ 0.53	$ 1.17
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 (1)	[2]	$ 0	$ 848	$ (215)	$ 5,151
Dilutive effect of Convertible Senior Notes		0	8,274	611	16,897
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	[1]	16	178	398	71
Stock Compensation Plan [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		676	1,045	440	1,045
Convertible Debt Securities [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount		0	0	0	1,902

[1] The following number of shares of our common stock equivalents issued under our share-based compensation arrangements and our convertible debt were not included in the calculation of diluted net income per share because they were anti-dilutive: Three Months EndedSeptember 30, Nine Months EndedSeptember 30,(In thousands)2017 2016 2017 2016Shares of common stock equivalents676 1,045 440 1,045Shares of Convertible Senior Notes due 2017— — — 1,902

[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.