Issued and Outstanding Preferred Shares and Preference Units - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Preferred Stock, Shares Authorized	100,000,000	100,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
8.29% Series K Cumulative Redeemable Preferred; liquidation value $50 per share; 745,600 shares issued and outstanding at December 31, 2016 and 2015	$ 37,280	$ 37,280
Premium on redemption of Preferred Shares	$ 0	$ (3,486)	$ 0
Series K Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock Preference Units Issued	745,600	745,600
Preferred Stock Preference Units Outstanding	745,600	745,600
Preferred Stock Preference Units Redemption Price Per Share Unit	$ 50.00	$ 50.00
Preferred Stock Preference Units Dividend Rate Percentage	8.29%	8.29%	8.29%
Preferred Stocks Preference Units Redemption Date	Dec. 10, 2026
Annual Dividend Per Preferred Share Preference Unit	$ 4.145
8.29% Series K Cumulative Redeemable Preferred; liquidation value $50 per share; 745,600 shares issued and outstanding at December 31, 2016 and 2015	$ 37,280	$ 37,280
Treasury Stock, Shares, Retired		254,400
Redemption of Preferred Shares		$ 12,700
Treasury Stock Retired, Cash Consideration		16,300
Premium on redemption of Preferred Shares		3,500
ERPOP [Member]
Class of Stock [Line Items]
8.29% Series K Cumulative Redeemable Preference Units; liquidation value $50 per unit; 745,600 units issued and outstanding at December 31, 2016 and 2015	37,280	37,280
Premium on redemption of Preferred Shares	$ 0	$ 3,486	$ 0
ERPOP [Member] | Series K Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock Preference Units Issued	745,600	745,600
Preferred Stock Preference Units Outstanding	745,600	745,600
Preferred Stock Preference Units Redemption Price Per Share Unit	$ 50.00	$ 50.00
Preferred Stock Preference Units Dividend Rate Percentage	8.29%	8.29%
Preferred Stocks Preference Units Redemption Date	Dec. 10, 2026
Annual Dividend Per Preferred Share Preference Unit	$ 4.145
8.29% Series K Cumulative Redeemable Preference Units; liquidation value $50 per unit; 745,600 units issued and outstanding at December 31, 2016 and 2015	$ 37,280	$ 37,280
Treasury Stock, Shares, Retired		254,400
Redemption of Preferred Shares		$ 12,700
Treasury Stock Retired, Cash Consideration		16,300
Premium on redemption of Preferred Shares		$ 3,500