Stockholders' Equity (Details) (USD $)	12 Months Ended				2 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2008	Feb. 19, 2015	May 31, 2012	May 31, 2007
Class of Stock [Line Items]
Shares Issued, Price Per Share	$ 29.95
Proceeds from Issuance of Common Stock	$ 102,100,000
Common stock, shares authorized	350,000,000	350,000,000
Preferred stock, shares authorized	50,000,000	50,000,000
Adjustment for conversion of non-controlling interest of unitholders in Operating Partnership, Shares	153,451
Common distributions declared per share	$ 1.040	$ 0.94	$ 0.88
Percentage distribution for not subject to domestic Federal income tax	0.90
Preferred stock, par or state value per share	$ 0	$ 0
Stock issued during period, shares, Distribution Reinvestment and Stock Purchase Plan				9,957,233
Shares reserved for issuance under the Stock Purchase Plan	10,963,730
Equity Distribution Agreement [Member]
Class of Stock [Line Items]
Common stock, shares authorized	20,000,000
Common Stock, Capital Shares Reserved for Future Issuance	16,518,567
Series E Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, liquidation preference per share	$ 16.61
Number of common stock shares to which each preferred share is convertible after special dividend	1.083
Declared preferred stock dividend	$ 1.33	$ 1.33	$ 1.33
Preferred stock, shares outstanding	2,803,812	2,803,812
Preferred stock, shares issued	2,803,812	2,803,812
Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares authorized	20,000,000
Preferred stock, shares outstanding	2,464,183
Preferred stock, par or state value per share	$ 0.0001
Preferred stock, value, issued	246
6.75% Series G Cumulative Redeemable Preferred Stock
Class of Stock [Line Items]
Declared preferred stock dividend	$ 0.00	$ 0.00	$ 0.57
Preferred stock, shares outstanding	0
Preferred stock, shares issued							5,400,000
Preferred stock, dividend rate			6.75%
Preferred stock, redemption price per share						$ 25
Stock stock, redemption amount						82,100,000
Preferred stock, shares redeemed			3,264,362
Preferred stock, redemption discount			2,791,000
Restricted Stock [Member]
Class of Stock [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other Than Options, Grants in Period Net of Forfeitures	860,811
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	873,010
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	12,199
Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	3,410,433		30,490,969
Issuance of stock during the period, shares, through Company’s 1999 Long-Term Incentive Plan, net of forfeitures	801,054	533,966	(22,224)
Adjustment for conversion of non-controlling interest of unitholders in Operating Partnership, Shares	153,451	76,291	20,438
Subsequent Event [Member]
Class of Stock [Line Items]
Shares Issued, Price Per Share					$ 32.28
Proceeds from Issuance of Common Stock					$ 110,800,000
Subsequent Event [Member] | Common Stock
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues					3,432,936