Equity - Preferred Stock (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Excess Tax Benefits from Share-Based Compensation	$ 946,000	$ 860,000	$ 0
Dividends, Preferred Stock, Cash	$ 13,182,000	$ 13,182,000	13,182,000
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	$ 1,700,000
Dividends, Preferred Stock, Cash	$ 0.3672
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	$ 1,900,000
Dividends, Preferred Stock, Cash		$ 0.4297
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	$ 1,600,000
Dividends, Preferred Stock, Cash			$ 0.3750
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%
July 17, 2024, thereafter [Member] | Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Variable Rate, Percentage	3.26%