Earnings Per Share (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 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	$ 182,043,000	$ 136,255,000	$ 685,413,000	$ 258,107,000
Denominator for basic earnings per share - weighted average shares	351,765,000	311,117,000	346,425,000	299,137,000
Effect of dilutive securities:
Employee stock options	114,000	202,000	155,000	181,000
Non-vested restricted shares	607,000	505,000	498,000	506,000
Redeemable shares	621,000	0	207,000	0
Convertible senior unsecured notes	0	988,000	262,000	821,000
Dilutive potential common shares	1,342,000	1,695,000	1,122,000	1,508,000
Denominator for diluted earnings per share - adjusted weighted average shares	353,107,000	312,812,000	347,547,000	300,645,000
Basic earnings per share	$ 0.52	$ 0.44	$ 1.98	$ 0.86
Diluted earnings per share	$ 0.52	$ 0.44	$ 1.97	$ 0.86