Note 5 - Earnings Per Common Share - Components Used in Computation of Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
1.625% Convertible Senior Notes due May 2018 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ 91		$ 1,088
Interest on convertible senior notes (in shares)	7,165,845		7,165,845
0.25% Convertible Senior Notes Due June 2019 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ 82		$ 984
Interest on convertible senior notes (in shares)	3,638,080		3,638,080
1.25% Convertible Senior Notes Due August 2032 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ 62	$ 41	$ 744	$ 490
Interest on convertible senior notes (in shares)	6,290,997	6,262,570	6,290,997	6,262,570
Net income	$ 132,348	$ 47,177	$ 317,769	$ 135,980
Less: Net income allocated to preferred shareholder		(11,342)		(32,818)
Less: Net income allocated to unvested restricted stock	(294)	(93)	(635)	(274)
Net income available to common stockholders for basic earnings per common share	132,054	35,742	317,134	102,888
Net income allocated to preferred shareholder		11,342		32,818
Net income available to common and preferred stock for diluted earnings per share	$ 132,289	$ 47,125	$ 319,950	$ 136,196
Basic (in shares)	118,338,891	55,345,443	119,188,145	55,059,683
Weighted average additional common shares outstanding if preferred shares converted to common shares (if dilutive) (in shares)		17,562,557		17,562,557
Total weighted average common shares outstanding if preferred shares converted to common shares (in shares)	118,338,891	72,908,000	119,188,145	72,622,240
Share-based awards (in shares)	643,602	684,511	605,860	830,501
Weighted average diluted shares outstanding (in shares)	136,077,415	79,855,081	136,888,927	79,715,311
Income Per Common Share:
Basic (in dollars per share)	$ 1.12	$ 0.65	$ 2.66	$ 1.87
Diluted (in dollars per share)	$ 0.97	$ 0.59	$ 2.34	$ 1.71