Real Estate Investments (Property Dispositions and Held for Sale Assets) (Narrative) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2016 USD ($) property	Jun. 30, 2015 USD ($) property	Dec. 31, 2015 property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds after debt assumptions and closing costs	$ 345,251	$ 324,949
Debt assumption	55,000	24,000
Goodwill allocated to dispositions	$ 36,141	47,499
2016 Property Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property	145
Aggregate proceeds	$ 381,300
Company's share of proceeds	102,100
Proceeds after debt assumptions and closing costs	303,000
Debt assumption	55,000
Gain (loss) related to sale, including goodwill	22,200
Goodwill included in sale	$ 21,500
Number of properties owned by consolidated joint ventures disposed of | property	1
Net proceeds	$ 113,500
Proceeds from after debt repayments and closing costs	42,300
Debt repayments	57,000
Gain related to sale of unconsolidated entities	$ 10,200
Number of properties classified held for sale | property	28
Net loss on sale of properties	$ (4,600)	(23,200)
Goodwill allocated to dispositions	$ 14,600	$ 17,800
Red Lobster [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property	24
Company's share of proceeds	$ 368,400
2015 Property Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property		15
Aggregate proceeds		$ 352,300
Proceeds after debt assumptions and closing costs		324,900
Gain (loss) related to sale, including goodwill		(32,800)
Goodwill included in sale		$ 29,700
Number of properties owned by consolidated joint ventures disposed of | property		1
Number of properties classified held for sale | property			17