Note 5 - Components Used in Computation of Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
1.625% Convertible Senior Notes due May 2018 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ 91		$ 453
Interest on convertible senior notes (in shares)	7,163,865		7,163,865
0.25% Convertible Senior Notes Due June 2019 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ 82		$ 410
Interest on convertible senior notes (in shares)	3,637,091		3,637,091
1.25% Convertible Senior Notes Due August 2032 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ 62	$ 41	$ 310	$ 204
Interest on convertible senior notes (in shares)	6,283,989	6,262,570	6,283,989	6,262,570
Net income	$ 112,760	$ 57,198	$ 185,421	$ 88,803
Less: Net income allocated to preferred shareholder		(13,798)		(21,475)
Less: Net income allocated to unvested restricted stock	(251)	(112)	(350)	(181)
Net income available to common stockholders for basic earnings per common share	112,509	43,288	185,071	67,147
Net income allocated to preferred shareholder		13,798		21,475
Net income available to common and preferred stock for diluted earnings per share	$ 112,744	$ 57,127	$ 186,244	$ 88,826
Basic (in shares)	118,419,937	55,099,690	119,617,438	54,914,435
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)	118,419,937	72,662,247	119,617,438	72,476,992
Share-based awards (in shares)	583,264	748,519	575,516	904,526
Weighted average diluted shares outstanding (in shares)	136,088,146	79,673,336	137,277,899	79,644,088
Income Per Common Share:
Basic (in dollars per share)	$ 0.95	$ 0.79	$ 1.55	$ 1.22
Diluted (in dollars per share)	$ 0.83	$ 0.72	$ 1.36	$ 1.12