Investments - Summary of Real Estate and Loan Activity, Net of Accumulated Depreciation and Amortization (Details) - Jun. 30, 2015
$ in Thousands
USD ($)
Property
Number of Properties  
Gross balance, December 31, 2014 | Property 2,509
Acquisitions/improvements | Property 148
Dispositions of real estate | Property (57)
Principal payments and payoffs | Property 0
Impairments | Property 0
Write off of gross lease intangibles | Property 0
Loan premium amortization and other | Property 0
Gross balance, June 30, 2015 | Property 2,600
Dollar Amount of Investments, net  
Gross balance, December 31, 2014 $ 8,044,363
Acquisitions/improvements 554,662
Dispositions of real estate (349,362)
Principal payments and payoffs (2,811)
Impairments (35,328)
Write off of gross lease intangibles (2,382)
Loan premium amortization and other (1,350)
Gross balance, June 30, 2015 8,207,792
Accumulated depreciation and amortization (983,229)
Other non-real estate assets held for sale 1,316
Net balance, June 30, 2015 $ 7,225,879
Owned Properties  
Number of Properties  
Gross balance, December 31, 2014 | Property 2,364
Acquisitions/improvements | Property 148
Dispositions of real estate | Property (57)
Principal payments and payoffs | Property 0
Impairments | Property 0
Write off of gross lease intangibles | Property 0
Loan premium amortization and other | Property 0
Gross balance, June 30, 2015 | Property 2,455
Dollar Amount of Investments, net  
Gross balance, December 31, 2014 $ 7,934,938
Acquisitions/improvements 550,662
Dispositions of real estate (349,362)
Principal payments and payoffs 0
Impairments (35,328)
Write off of gross lease intangibles (2,382)
Loan premium amortization and other (113)
Gross balance, June 30, 2015 8,098,415
Accumulated depreciation and amortization (983,229)
Other non-real estate assets held for sale 1,316
Net balance, June 30, 2015 $ 7,116,502
Financed Properties  
Number of Properties  
Gross balance, December 31, 2014 | Property 145
Acquisitions/improvements | Property 0
Dispositions of real estate | Property 0
Principal payments and payoffs | Property 0
Impairments | Property 0
Write off of gross lease intangibles | Property 0
Loan premium amortization and other | Property 0
Gross balance, June 30, 2015 | Property 145
Dollar Amount of Investments, net  
Gross balance, December 31, 2014 $ 109,425
Acquisitions/improvements 4,000
Dispositions of real estate 0
Principal payments and payoffs (2,811)
Impairments 0
Write off of gross lease intangibles 0
Loan premium amortization and other (1,237)
Gross balance, June 30, 2015 109,377
Accumulated depreciation and amortization 0
Other non-real estate assets held for sale 0
Net balance, June 30, 2015 $ 109,377