Shareholders' Equity - Common and Preferred Units (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Temporary Equity [Line Items]
Noncontrolling Interest Operating Partnership Common Units Outstanding	3,556,566	3,713,851
Redeemable Noncontrolling Interest, Equity, Common, Fair Value	$ 120,500,000
Preferred Units Description and Other Disclosures [Abstract]
Preferred Stock Redemption Premium	1,236,000
Preferred Stock Redemption Discount		3,689,000
Preferred Units, Total Annual Cash Distributions	1,600,000.0	9,900,000.0	21,000,000.00
Authorized but Unissued Preferred Shares	16,013,000
Preferred Units, Outstanding	0	1,290,000
Conversion Ratio of Common Units to Common Shares [Member]
Temporary Equity [Line Items]
Common Unit, Convertible to Common Stock	1
Common Stock, Converted from Common Unit	1
Common Units [Member]
Temporary Equity [Line Items]
Common Units Issued in Connection with Acquisitions	0	0	0
Series B Preferred Stock [Member]
Preferred Units Description and Other Disclosures [Abstract]
Stock Redeemed or Called During Period, Value		95,000,000
Preferred Stock Dividends Rate Percentage Or Per Dollar Amount		7.45%
Preferred Units, Annual Cash Distributions	$ 0.00	$ 0.45	$ 1.86
Series E Preferred Stock [Member]
Preferred Units Description and Other Disclosures [Abstract]
Stock Redeemed or Called During Period, Value	20,000,000
Preferred Stock Dividends Rate Percentage Or Per Dollar Amount	7.00%
Preferred Units, Annual Cash Distributions	$ 1.21	$ 3.50	$ 3.50
Series F Preferred Stock [Member]
Preferred Units Description and Other Disclosures [Abstract]
Stock Redeemed or Called During Period, Value	17,500,000	32,500,000
Payments for Repurchase of Preferred Stock and Preference Stock		26,000,000
Preferred Stock Dividends Rate Percentage Or Per Dollar Amount	6.65%	6.65%
Preferred Units, Annual Cash Distributions	$ 1.32	$ 1.43	$ 3.33
Series G Preferred Stock [Member]
Preferred Units Description and Other Disclosures [Abstract]
Stock Redeemed or Called During Period, Value	27,000,000
Preferred Stock Dividends Rate Percentage Or Per Dollar Amount	6.70%
Preferred Units, Annual Cash Distributions	$ 1.33	$ 3.35	$ 3.35
Series H Preferred Stock [Member]
Preferred Units Description and Other Disclosures [Abstract]
Stock Redeemed or Called During Period, Value		$ 100,000,000
Preferred Stock Dividends Rate Percentage Or Per Dollar Amount		7.40%
Preferred Units, Annual Cash Distributions	$ 0.00	$ 0.77	$ 1.85