Equity (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Balance
Total stockholders' equity			$ 2,823,164
Noncontrolling interest			32,738
Total equity			2,855,902	2,648,248
Net loss attributable to noncontrolling interest	(779)	(179)	(1,302)	(179)
Net income (loss)	53,327	46,333	109,466	102,848
Other comprehensive income	340	(206)	1,007	(8,100)
Dividends declared on preferred stocks			(342)	(342)
Dividends declared on common stock			(68,025)	(65,147)
Stock-based compensation			2,796	2,453
Issuance of common stock upon vesting of performance shares, net of shares used for tax withholdings			(5,564)
Net tax benefit on stock-based compensation			4,729	(1,419)
Issuance of common stock			131,973
Contribution from noncontrolling interest			32,500	16,101
Total stockholders' equity	3,000,506	2,678,720	3,000,506	2,678,720
Noncontrolling interest	63,936	15,922	63,936	15,922
Total equity	3,064,442	2,694,642	3,064,442	2,694,642
Total stockholders’ equity [Member]
Balance
Total stockholders' equity			2,823,164	2,648,248
Net income (loss) attributable to parent			110,768	103,027
Other comprehensive income			1,007	(8,100)
Dividends declared on preferred stocks			(342)	(342)
Dividends declared on common stock			(68,025)	(65,147)
Stock-based compensation			2,796	2,453
Issuance of common stock upon vesting of performance shares, net of shares used for tax withholdings			(5,564)
Net tax benefit on stock-based compensation			4,729	(1,419)
Issuance of common stock			131,973
Contribution from noncontrolling interest			0	0
Total stockholders' equity	3,000,506	2,678,720	3,000,506	2,678,720
Noncontrolling interest [Member]
Balance
Noncontrolling interest			32,738	0
Net loss attributable to noncontrolling interest			(1,302)	(179)
Other comprehensive income			0	0
Dividends declared on preferred stocks			0	0
Dividends declared on common stock			0	0
Stock-based compensation			0	0
Issuance of common stock upon vesting of performance shares, net of shares used for tax withholdings			0
Net tax benefit on stock-based compensation			0	0
Issuance of common stock			0
Contribution from noncontrolling interest			32,500	16,101
Noncontrolling interest	$ 63,936	$ 15,922	$ 63,936	$ 15,922