Business Combinations (Unaudited Pro forma Information) (Details) (Parent Company [Member], USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Business Acquisition [Line Items]
Payments To Acquire Real Estate And Other Assets	$ 139,199,000		$ 312,001,000		$ 362,745,000
Purchase price for Colonial merger	2,162,876,000		0		0
Total Revenue	941,662,000	[1]	844,002,000	[1]
Net Income available to common shareholders	142,593,000	[1]	100,752,000	[1]
Earnings per share, diluted (dollars per share)	$ 1.78	[1]	$ 1.45	[1]
Business Combination, Merger and Integration Related Expenses	37,500,000
Colonial
Business Acquisition [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	104,000,000
Business Acquisition, Purchase Price Allocation, Assets Acquired	4,056,921,000
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	(1,894,045,000)
Purchase price for Colonial merger	2,200,000,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	17,600,000
Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Payments To Acquire Real Estate And Other Assets	(139,200,000)
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	8,700,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	4,200,000
Land | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	469,396,000
Land | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	26,900,000
Building and Building Improvements | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	3,069,642,000
Building and Building Improvements | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	125,700,000
Furniture Fixtures And Equipment | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	96,377,000
Furniture Fixtures And Equipment | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	300,000
Construction in Progress | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	113,368,000
Unimproved Land | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	58,400,000
Assets Held-for-sale | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	33,800,000
Finite-Lived Intangible Assets, Major Class Name | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	57,946,000
Finite-Lived Intangible Assets, Major Class Name | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	1,200,000
Cash and Cash Equivalents | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	63,454,000
Restricted Cash | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	6,825,000
Other Assets | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	87,713,000
Other Assets | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Assets Acquired	100,000
Debt | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	(1,759,550,000)
Interest Rate Cash Flow Hedge Liability at Fair Value | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	(14,961,000)
Other Liabilities | Colonial
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	(119,534,000)
Other Liabilities | Series of Individually Immaterial Business Acquisitions
Business Acquisition [Line Items]
Business Acquisition, Purchase Price Allocation, Liabilities Assumed	$ (900,000)

[1] Pro forma adjustments for certain acquisitions are excluded as they had no pre-acquisition operating activity in 2012 or 2013.