Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Computation of basic and diluted earnings per share
Numerator for basic and diluted earnings per share - net income (loss) attributable to common stockholders	$ 54,735		$ 69,847		$ 94,037		$ 93,219
Denominator for basic earnings per share - weighted average shares	213,498,000		176,445,000		206,612,000		165,755,000
Effect of dilutive securities:
Employee stock options	261,000		178,000		242,000		184,000
Non-vested restricted shares	299,000		249,000		290,000		232,000
Convertible senior unsecured notes	1,080,000		616,000		1,093,000		287,000
Dilutive potential common shares	1,640,000		1,043,000		1,625,000		703,000
Denominator for diluted earnings per share - adjusted weighted average shares	215,138,000		177,488,000		208,237,000		166,458,000
Basic earnings per share	$ 0.26	[1]	$ 0.40	[1]	$ 0.46	[1]	$ 0.56	[1]
Diluted earnings per share	$ 0.25	[1]	$ 0.39	[1]	$ 0.45	[1]	$ 0.56	[1]
Earnings Per Share (Textual) [Abstract]
Securities Excluded From Computation Of Diluted Earnings Per Share	354,000		287,000		366,000		287,000

[1] Amounts may not sum due to rounding