Note 2 - Summary of Significant Accounting Policies (Details) - Computation of Basic and Diluted Earnings Per Share - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Numerator:
Net income	$ 77,529	$ 47,177	$ 57,198	$ 31,605	$ 64,644	$ 56,599	$ 56,463	$ 38,159	$ 213,509	[1]	$ 215,865	[1]	$ 188,715
Less: Net income allocated to preferred shareholder									(32,997)		(51,650)		(57,386)
Less: Net income allocated to unvested restricted stock									(369)		(297)		(265)
Net income available to common stockholders for basic earnings per common share									180,143		163,918		131,064
Effect of dilutive securities:
Net income allocated to preferred shareholder									32,997		51,650		57,386
Net income available to common and preferred stock for diluted earnings per share									$ 214,094		$ 216,467		$ 189,349
Denominator:
Weighted average basic common shares outstanding (in Shares)									71,713,747		55,737,548		50,623,649
Weighted average additional common shares outstanding if preferred shares converted to common shares (if dilutive) (in Shares)									13,135,814		17,562,557		22,165,311
Total weighted average common shares outstanding if preferred shares converted to common shares (in Shares)									84,849,561		73,300,105		72,788,961
Effect of dilutive securities:
Share-based awards (in Shares)									816,459		1,256,964		1,348,571
Weighted average diluted shares outstanding (in Shares)									94,648,767		80,819,639		80,400,102
Income per share:
Basic (in Dollars per share)	$ 0.64	$ 0.65	$ 0.80	$ 0.45	$ 0.88	$ 0.77	$ 0.75	$ 0.50	$ 2.51	[1]	$ 2.94	[1]	$ 2.59
Diluted (in Dollars per share)	$ 0.56	$ 0.59	$ 0.70	$ 0.40	$ 0.80	$ 0.70	$ 0.70	$ 0.45	$ 2.26	[1]	$ 2.68	[1]	$ 2.36
1.625% Convertible Senior Notes Due May 2018 [Member]
Effect of dilutive securities:
Interest on convertible senior notes									$ 47
Effect of dilutive securities:
Share-based awards on convertible senrio notes (in Shares)									1,804,192
0.25% Convertible Senior Notes Due June 2019 [Member]
Effect of dilutive securities:
Interest on convertible senior notes									$ 9
Effect of dilutive securities:
Share-based awards on convertible senrio notes (in Shares)									915,985
1¼% Convertible Senior Notes Due August 2032 [Member]
Effect of dilutive securities:
Interest on convertible senior notes									$ 898		$ 899		$ 899
Effect of dilutive securities:
Share-based awards on convertible senrio notes (in Shares)									6,262,570		6,262,570		6,262,570

[1] Per share amounts do not add across due to rounding differences in quarterly amounts and due to the impact of differences between the quarterly and annual weighted average share calculations.