Equity - Narrative (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended						6 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2014 class_of_stock	Jun. 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	$ 0.12	$ 0.12	$ 0.12	$ 0.12	$ 0.28	$ 0.24
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%