Equity (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Changes in equity
Balance at the beginning of the period	$ 4,401,892,000
Net income attributable to common stockholders	57,704,000
Unrealized gain on cash flow hedges	11,008,000	(84,000)
Change in redemption value of redeemable noncontrolling interest	(309,000)	(981,000)
Dividends declared to common stockholders	(92,481,000)
Issuance of common stock, net of withholdings	3,608,000
Amortization of deferred compensation	8,848,000
Balance at the end of the period	4,390,270,000
Common stock
Changes in equity
Balance at the beginning of the period	952,000
Issuance of common stock, net of withholdings	1,000
Balance at the end of the period	953,000
Additional paid-in capital
Changes in equity
Balance at the beginning of the period	4,652,457,000
Issuance of common stock, net of withholdings	5,231,000
Amortization of deferred compensation	8,848,000
Balance at the end of the period	4,666,536,000
Accumulated earnings less dividends
Changes in equity
Balance at the beginning of the period	(171,648,000)
Net income attributable to common stockholders	57,758,000
Change in redemption value of redeemable noncontrolling interest	(309,000)
Dividends declared to common stockholders	(92,481,000)
Issuance of common stock, net of withholdings	(1,624,000)
Balance at the end of the period	(208,304,000)
Accumulated other comprehensive gain (loss)
Changes in equity
Balance at the beginning of the period	(87,020,000)
Unrealized gain on cash flow hedges	11,008,000
Balance at the end of the period	(76,012,000)
Total stockholders' equity
Changes in equity
Balance at the beginning of the period	4,394,741,000
Net income attributable to common stockholders	57,758,000
Unrealized gain on cash flow hedges	11,008,000
Change in redemption value of redeemable noncontrolling interest	(309,000)
Dividends declared to common stockholders	(92,481,000)
Issuance of common stock, net of withholdings	3,608,000
Amortization of deferred compensation	8,848,000
Balance at the end of the period	4,383,173,000
Noncontrolling interests
Changes in equity
Balance at the beginning of the period	7,151,000
Net income attributable to common stockholders	(54,000)
Balance at the end of the period	$ 7,097,000