Real Estate Investments (Property Dispositions and Held for Sale Assets) (Narrative) (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2016 USD ($) property	Sep. 30, 2015 USD ($) property	Dec. 31, 2015 property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property	35
Proceeds after debt assumptions and closing costs	$ 615,246	$ 413,270
Debt assumption	55,000	300,720
Goodwill allocated to dispositions	53,764	$ 66,789
Mortgages [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt repayments	$ 227,503
Consolidated Property Dispositions, 2016 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property	223
Aggregate proceeds	$ 672,500
Company's share of proceeds	646,400
Proceeds after debt assumptions and closing costs	573,000
Gain (loss) related to sale, including goodwill	50,700
Goodwill included in sale	28,800
Consolidated Property Dispositions, 2016 [Member] | Mortgages [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt assumption	$ 55,000
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	47
Consolidated Property Dispositions, 2015 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property		88
Aggregate proceeds		$ 675,900
Proceeds after debt assumptions and closing costs		370,200
Gain (loss) related to sale, including goodwill		(39,300)
Goodwill included in sale		$ 48,500
Number of properties owned by consolidated joint ventures disposed of | property		1
Net proceeds		$ 77,500
Proceeds from after debt repayments and closing costs		43,000
Gain related to sale of unconsolidated entities		$ 6,700
Unconsolidated Property Dispositions, 2016 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Company's share of proceeds	$ 102,100
Number of disposed properties owned by unconsolidated joint ventures | 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
Unconsolidated Property Dispositions, 2015 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of disposed properties owned by unconsolidated joint ventures | property		3
2016 Property Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified held for sale | property	19
Net loss on sale of properties	$ (5,000)	$ (23,300)
Goodwill allocated to dispositions	$ 22,700	$ 18,300
2015 Property Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties classified held for sale | property			17