Real Estate Investments (Property Dispositions and Held for Sale Assets) (Narrative) (Details) $ in Thousands		12 Months Ended
	Jan. 29, 2015 property	Dec. 31, 2015 USD ($) property joint_venture	Dec. 31, 2014 USD ($) property	Dec. 31, 2013 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds after debt assumptions and closing costs		$ 1,009,107	$ 1,598,767	$ 0
Loss related to sale of properties, included in loss on disposition of real estate and held for sale assets, net		(72,311)	(277,031)	0
Foreclosed upon property net book value		15,006,124	17,258,438
Gain on sale of consolidated joint venture		$ 6,729	$ 0	$ 0
Number of properties classified held for sale | property		17	2
Goodwill allocated to dispositions		$ 98,765	$ 210,139
REI Segment [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Goodwill allocated to dispositions		$ 98,765	$ 210,139
REI Segment [Member] | Unconsolidated Properties [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of unconsolidated joint ventures | joint_venture		3
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		228
Number of properties owned by consolidated joint ventures disposed of | property		2
Aggregate proceeds		$ 1,400,000
Proceeds after debt assumptions and closing costs		966,100
Loss related to sale of properties, included in loss on disposition of real estate and held for sale assets, net		(72,300)
Goodwill allocated in cost basis		$ 98,800
Number of properties classified held for sale | property		17	2
Net loss on sale of properties		$ 3,200
Goodwill allocated to dispositions		$ 2,100
2015 Property Dispositions [Member] | Consolidated Joint Venture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties owned by consolidated joint ventures disposed of | property	1	1
Company's share of proceeds		$ 69,800
Proceeds after debt repayment and closing costs		43,000
Gain on sale of consolidated joint venture		$ 6,700
Foreclosed Upon Real Estate Property [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties foreclosed upon | property		1
Foreclosed upon property net book value		$ 38,200
2014 Property Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Aggregate proceeds			$ 1,600,000
2014 Property Dispositions [Member] | Single-Tenant Property [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property			45
2014 Property Dispositions [Member] | Anchored Shopping Center [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property			65
Variable Interest Entity, Primary Beneficiary | 2015 Property Dispositions [Member] | Consolidated Joint Venture [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net proceeds		$ 77,500