Equity (Details Textual) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 29, 2012	Oct. 31, 2013	Mar. 31, 2013	Jul. 31, 2012	Jun. 30, 2013	Apr. 30, 2013
Stockholders Equity [Line Items]
Preferred Stock Dividend Rate Percentage	8.00%	8.00%	100.00%
Operating Partnership Units Outstanding	65,100,000
Dividend Declared Per Preferred Share	$ 0.50
Accrued Dividends Preferred Stock	$ 3,100,000
Dividends paid to common and preferred stockholders	250,000	287,000	281,000
Preferred stock, liquidation preference per share	$ 25.00	$ 25.00
Restatement To Increase In Authorized Shares Of Common Stock									500,000,000
Restatement To Increase In Authorized Shares Of Preferred Stock									550,000,000
Preferred Stock, Shares Authorized	50,000,000	50,000,000							50,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01							$ 0.01
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01							$ 0.01
Maximum shares issue value under market offering program								100,000,000
Issuance of preferred stock		299,719,000	72,162,000
Board Of Directors [Member]
Stockholders Equity [Line Items]
Dividend Declared Per Common Share and Operating Partnership Unit	$ 0.090
Dividend Paid [Member]
Stockholders Equity [Line Items]
Dividend Declared Per Common Share and Operating Partnership Unit	$ 0.585	$ 0.66	$ 0.64
Dividends paid to common and preferred stockholders	38,100,000	42,900,000	22,600,000
Parent Company [Member]
Stockholders Equity [Line Items]
Operating Partnership Units Outstanding	64,700,000
Percentage Of Operating Partnership Units Held	99.30%
Other Partners [Member]
Stockholders Equity [Line Items]
Operating Partnership Units Outstanding	400,000
Percentage Of Operating Partnership Units Held	0.70%
Fair Market Value Of Operating Partnership Units	2,900,000
Per Unit Fair Market Value Of Operating Partnership Units	$ 7.31
8% Series A Cumulative Redeemable Preferred Stock [Member]
Stockholders Equity [Line Items]
Preferred Stock Dividend Rate Percentage	8.00%
Stock Issued During Period, Shares, New Issues				300,000
Preferred stock, liquidation preference per share	$ 25.00
Preferred Stock Dividend Rate Per Dollar Amount	$ 2.00
Preferred Stock Redemption Price Per Share	$ 25.00
Preferred Stock Public Offering Price				$ 25.00
Issuance of preferred stock				54,900,000
Repayments of Long-term Debt				48,900,000
Preferred Stock Underwritten Public Offerings				2,300,000
Stock Issued For Underwritten Public Offering Value				2,600,000
Series A Preferred Stock [Member]
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, New Issues					400,000
Dividend Declared Per Preferred Share	$ 2.00	$ 2.00
Dividends paid to common and preferred stockholders	12,200,000	6,500,000
Preferred Stock Public Offering Price					$ 25.0611
Issuance of preferred stock					91,300,000
Repayments of Long-term Debt					46,800,000
Preferred Stock Underwritten Public Offerings					3,800,000
Stock Issued For Underwritten Public Offering Value					4,000,000
IPO [Member]
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, New Issues						25,500,000	7,500,000
Proceeds from Issuance Initial Public Offering						$ 299,700,000	$ 72,200,000
Underwriters Option [Member]
Stockholders Equity [Line Items]
Stock Issued During Period, Shares, New Issues						3,300,000	1,000,000