Note 5 - Components Used in Computation of Basic and Diluted Earnings Per Common Share (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
1.625% convertible senior notes due 2018 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ (370)
Weighted Average Common Shares Outstanding:
Common shares attributable to dilutive effect of conversion of senior notes (in shares)	7,157,934
0.25% Convertible Senior Notes Due June 2019 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ 82
Weighted Average Common Shares Outstanding:
Common shares attributable to dilutive effect of conversion of senior notes (in shares)	3,634,072
1.25% Convertible Senior Notes Due August 2032 [Member]
Effect of dilutive securities:
Interest on convertible senior notes	$ 62	$ 41
Weighted Average Common Shares Outstanding:
Common shares attributable to dilutive effect of conversion of senior notes (in shares)	6,262,570	6,262,570
Net income	$ 72,661,000	$ 31,605,000
Less: Net income allocated to preferred shareholder		(7,662,000)
Less: Net income allocated to unvested restricted stock	$ (113,000)	(67,000)
Net income available to common stockholders for basic earnings per common share	$ 72,548,000	23,876,000
Net income allocated to preferred shareholder		7,662,000
Net income available to common and preferred stock for diluted earnings per share	$ 72,322,000	$ 31,579,000
Basic (in shares)	120,814,939	54,727,121
Weighted average additional common shares outstanding if preferred shares converted to common shares (if dilutive) (in shares)		17,562,557
Total weighted average common shares outstanding if preferred shares converted to common shares (in shares)	120,814,939	72,289,678
Share-based awards (in shares)	561,065	1,088,673
Weighted average diluted shares outstanding (in shares)	138,430,580	79,640,921
Income Per Common Share:
Basic (in dollars per share)	$ 0.60	$ 0.44
Diluted (in dollars per share)	$ 0.52	$ 0.40