Real Estate Investments - Property Dispositions and Held for Sale Assets Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) property	Dec. 31, 2015 USD ($) property joint_venture	Dec. 31, 2014 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of real estate properties disposed | property	101	228
Proceeds after debt assumptions and closing costs	$ 1,000,700	$ 1,009,107	$ 1,598,767
Debt assumption	55,000	425,021	$ 461,111
Goodwill allocated to dispositions	73,240	$ 98,765
Mortgages [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Debt repayments	$ 413,045
2016 Consolidated 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	301
Aggregate proceeds	$ 1,080,000
Company's share of proceeds	1,040,000
Proceeds after debt assumptions and closing costs	958,400
Gain related to sale of unconsolidated entities	45,700
Goodwill allocated to dispositions	67,800
2016 Consolidated Property Dispositions [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	70
2016 Unconsolidated Property Dispositions [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
2016 Unconsolidated Property Dispositions [Member] | Income (Loss) from Equity Method Investments and Realized Gain (Loss) on Disposal [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain related to sale of unconsolidated entities	$ 10,200
2015 Consolidated 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		2
Aggregate proceeds		$ 1,400,000
Company's share of proceeds		69,800
Proceeds after debt assumptions and closing costs		966,100
Gain (loss) related to sale, including goodwill		(69,100)
Goodwill included in sale		96,700
Net proceeds		77,500
Proceeds from after debt repayments and closing costs		$ 43,000
Number of properties owned by consolidated joint ventures disposed of | property		1
2015 Consolidated Property Dispositions [Member] | Income (Loss) from Equity Method Investments and Realized Gain (Loss) on Disposal [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain related to sale of unconsolidated entities		$ 6,700
2015 Unconsolidated Property Dispositions [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of unconsolidated joint ventures | joint_venture		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	11
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
Net loss on sale of properties	$ 200	$ 3,200
Goodwill allocated to dispositions	$ 3,200	$ 2,100