Earnings Per Share (Details) (USD $) In Thousands, except Share data	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010
Computation of basic and diluted earnings per share
Numerator for basic and diluted earnings per share - net income attributable to common stockholders	$ 69,847		$ 45,646		$ 93,219		$ 71,458
Denominator for basic earnings per share - weighted average shares	176,445,000		123,808,000		165,755,000		123,541,000
Effect of dilutive securities:
Employee stock options	178,000		102,000		184,000		104,000
Non-vested restricted shares	249,000		414,000		232,000		414,000
Convertible senior unsecured notes	616,000				287,000
Dilutive potential common shares	1,043,000		516,000		703,000		518,000
Denominator for diluted earnings per share - adjusted weighted average shares	177,488,000		124,324,000		166,458,000		124,059,000
Basic earnings per share	$ 0.40	[1]	$ 0.37	[1]	$ 0.56	[1]	$ 0.58	[1]
Diluted earnings per share	$ 0.39	[1]	$ 0.37	[1]	$ 0.56	[1]	$ 0.58	[1]
Earnings Per Share (Textuals) [Abstract]
Securities Excluded From Computation Of Diluted Earnings Per Share	287,000		381,000		287,000		381,000

[1] Amounts may not sum due to rounding