Shareholders' Equity Preferred Stock (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock	$ 0	$ 0	$ 446,592,000
Other Preferred Stock Dividends and Adjustments	$ 0	$ 0	13,752,000
Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock			$ 17,700,000
Preferred Stock, Redemption Price Per Share			$ 250
Stock Repurchased During Period, Shares			750,243
Stock Repurchased During Period, Value			$ 18,800,000
Series J Preferred Stock [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock			96,100,000
Other Preferred Stock Dividends and Adjustments			$ 3,200,000
Stock Redeemed or Called During Period, Shares			384,530
Preferred Stock, Dividend Rate, Percentage			6.625%
Series K Preferred Stock [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock			$ 149,400,000
Other Preferred Stock Dividends and Adjustments			$ 5,000,000
Stock Redeemed or Called During Period, Shares			597,579
Preferred Stock, Dividend Rate, Percentage			6.50%
Series L Preferred Stock [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Payments for Repurchase of Redeemable Preferred Stock			$ 183,400,000
Other Preferred Stock Dividends and Adjustments			$ 6,000,000
Stock Redeemed or Called During Period, Shares			733,597
Preferred Stock, Dividend Rate, Percentage			6.60%
Issuance Costs [Member] | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Other Preferred Stock Dividends and Adjustments			$ 618,000
Gain (Loss) Repurchase of Redeemable Preferred Shares (Member) | Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Other Preferred Stock Dividends and Adjustments			$ (483,000)