Equity - Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued	3,000,000	3,000,000
Preferred stock, par value	$ 25	$ 25
Payments of Stock Issuance Costs	$ 1.6
Preferred Stock, Shares Outstanding	3,000,000	3,000,000
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued	3,000,000	3,000,000
Preferred Stock, Dividend Rate, Percentage	6.875%
Preferred stock, par value	$ 25	$ 25
Payments of Stock Issuance Costs	$ 1.9
Preferred Stock, Shares Outstanding	3,000,000	3,000,000
Series A Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Shares Issued	2,400,000	2,400,000
Preferred Stock, Dividend Rate, Percentage	5.875%
Preferred stock, par value	$ 25	$ 25
Preferred Stock, Liquidation Preference Per Share	$ 25
Payments of Stock Issuance Costs	$ 1.7
Preferred Stock, Shares Outstanding	2,400,000	2,400,000
July 17, 2024, thereafter [Member] | Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Variable Rate, Percentage	3.26%
Up to but excluding July 17, 2024 [Member] | Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage	6.00%