Income Taxes (Reconciliation of Net Income to REIT Taxable Income) (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Abstract]
Net income										$ 293,900,000	$ 59,961,000	$ 31,142,000
Less income allocated to non-controlling interests from continuing operations										4,821,000	3,453,000	821,000
Less income, including gain on sale, allocated to non-controlling interests from discontinued operations										2,838,000	129,000	105,000
Less income allocated to perpetual preferred units										776,000	7,000,000	7,000,000
Write off of original issuance costs of redeemed perpetual preferred units										2,075,000	0	0
Net income attributable to common shareholders	142,166,000	30,703,000	21,763,000	88,758,000	46,850,000	11,840,000	(16,597,000)	7,286,000		283,390,000	49,379,000	23,216,000
Loss from taxable Real Estate Investment Trust subsidiaries included above										3,323,000	539,000	2,056,000
Net income from Real Estate Investment Trust operations										286,713,000	49,918,000	25,272,000
Book depreciation and amortization, including discontinued operations										213,479,000	188,042,000	179,662,000
Tax depreciation and amortization										(171,060,000)	(155,636,000)	(158,134,000)
Book/tax difference on gains/losses from capital transactions										(63,832,000)	(4,315,000)	37,798,000
Other book/tax differences, net										(40,961,000)	8,205,000	(10,565,000)
Real Estate Investment Trust Taxable Income										224,339,000	86,214,000	74,033,000
Dividends paid deduction										(224,339,000)	(143,657,000)	(124,999,000)
Dividends Paid In Excess Of Taxable Income										0	(57,443,000)	(50,966,000)
Income tax reconciliation, designated dividends included in dividends paid deduction									$ 33,300,000