Earnings Per Share (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Computation of basic and diluted earnings per share
Numerator for basic and diluted earnings per share - net income (loss) attributable to common stockholders	$ 312,573,000	$ 71,829,000	$ 503,373,000	$ 121,851,000
Denominator for basic earnings per share - weighted average shares	350,399,000	296,256,000	343,624,000	293,046,000
Effect of dilutive securities:
Employee stock options	153,000	191,000	176,000	170,000
Non-vested restricted shares	471,000	472,000	444,000	506,000
Convertible senior unsecured notes	343,000	1,076,000	379,000	868,000
Dilutive potential common shares	967,000	1,739,000	999,000	1,544,000
Denominator for diluted earnings per share - adjusted weighted average shares	351,366,000	297,995,000	344,623,000	294,590,000
Basic earnings per share	$ 0.89	$ 0.24	$ 1.46	$ 0.42
Diluted earnings per share	$ 0.89	$ 0.24	$ 1.46	$ 0.41
Earnings Per Share (Textual) [Abstract]
Securities Excluded From Computation Of Diluted Earnings Per Share	0	0	0