Equity - Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended							9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2014 class_of_stock	Sep. 30, 2013
Class of Stock [Line Items]
Number of Classes of Common Stock								3
Common stock dividend, per share, cash paid	$ 0.14	$ 0.14	$ 0.14	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.42	$ 0.36
Common Class A, Voting [Member]
Class of Stock [Line Items]
Common Stock, Maximum Ownership Percentage by a Beneficial Owner	33.00%							33.00%
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, shares issued	2,400,000			2,400,000				2,400,000
Preferred Stock, shares outstanding	2,400,000			2,400,000				2,400,000
Preferred Stock, Dividend Rate, Percentage								5.875%
Payments of Stock Issuance Costs									$ 1.7
Preferred Stock, Par or Stated Value Per Share	$ 25			$ 25				$ 25
Preferred Stock, Liquidation Preference Per Share	$ 25							$ 25
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, shares issued	3,000,000			0				3,000,000
Preferred Stock, shares outstanding	3,000,000			0				3,000,000
Preferred Stock, Dividend Rate, Percentage								6.875%
Payments of Stock Issuance Costs								1.9
Preferred Stock, Par or Stated Value Per Share	$ 25			$ 0				$ 25
Preferred Stock, Liquidation Preference Per Share	$ 25							$ 25
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, shares issued	3,000,000			0				3,000,000
Preferred Stock, shares outstanding	3,000,000			0				3,000,000
Preferred Stock, Dividend Rate, Percentage								6.00%
Payments of Stock Issuance Costs								$ 1.6
Preferred Stock, Par or Stated Value Per Share	$ 25			$ 0				$ 25
Preferred Stock, Liquidation Preference Per Share	$ 25							$ 25
Retired Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Par or Stated Value Per Share	$ 1,000							$ 1,000
Preferred Stock, Liquidation Preference Per Share	$ 1,000							$ 1,000
July 17, 2024, thereafter [Member] | Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Variable Rate, Percentage								3.26%