Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 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	$ 37,269		$ 36,607		$ 131,308		$ 129,826
Denominator for basic earnings per share - weighted average shares	224,391,000		177,272,000		212,592,000		169,636,000
Effect of dilutive securities:
Employee stock options	238,000		172,000		240,000		180,000
Non-vested restricted shares	301,000		258,000		293,000		241,000
Convertible senior unsecured notes	1,328,000		147,000		950,000		244,000
Dilutive potential common shares	1,867,000		577,000		1,483,000		665,000
Denominator for diluted earnings per share - adjusted weighted average shares	226,258,000		177,849,000		214,075,000		170,301,000
Basic earnings per share	$ 0.17	[1]	$ 0.21	[1]	$ 0.62	[1]	$ 0.77	[1]
Diluted earnings per share	$ 0.16	[1]	$ 0.21	[1]	$ 0.61	[1]	$ 0.76	[1]
Earnings Per Share (Textual) [Abstract]
Securities Excluded From Computation Of Diluted Earnings Per Share	237,000		227,000		0		381,000

[1] Amounts may not sum due to rounding