Summary of Significant Accounting Policies - Additional Information (Details)
12 Months Ended
Dec. 31, 2017
USD ($)
Loan
receivable
segment
Dec. 31, 2016
USD ($)
Loan
receivable
Dec. 31, 2015
USD ($)
Lease
Summary Of Significant Accounting Policies [Line Items]      
Net assets $ 7,263,511,000 $ 7,677,971,000  
Net liabilities $ 3,943,902,000 3,995,863,000  
Number of operating segments | segment 1    
Amounts past due $ 0 0  
Impairments or allowances of direct financing lease $ 0 0 $ 4,800,000
Number of direct financing leases with impairments | Lease     2
Rent escalators adjustment period 1 year    
Threshold period for past due amounts 60 days    
Impairment on existing goodwill $ 0 0 $ 0
Goodwill written off from disposal of real estate assets not previously classified as held for sale 0 10,010,000 21,498,000
Reserves for uncollectible amounts 12,400,000 6,400,000  
Accounts receivable 27,200,000 25,300,000  
Provision for losses 1,800,000 7,700,000  
Accrued rental revenue receivables 81,600,000 71,100,000  
Allowance for loan losses $ 400,000 $ 500,000  
Loan placed on non accrual status, past due days 60 days    
Number of loans on nonaccrual status | Loan 5 0  
Receivables, nonaccrual status $ 1,500,000 $ 500,000  
Number of notes receivable on nonaccrual status | receivable 0 1  
Federal income tax $ 0    
Discontinued Operations, Disposed of by Sale      
Summary Of Significant Accounting Policies [Line Items]      
Goodwill written off from disposal of real estate assets not previously classified as held for sale   $ 6,300,000 12,700,000
Interest income and other      
Summary Of Significant Accounting Policies [Line Items]      
Lease termination fee $ 5,000,000 7,300,000 $ 5,800,000
Minimum      
Summary Of Significant Accounting Policies [Line Items]      
Rent escalator increase as ratio of CPI 1    
Maximum      
Summary Of Significant Accounting Policies [Line Items]      
Rent escalator increase as ratio of CPI 2    
Building and improvements | Minimum      
Summary Of Significant Accounting Policies [Line Items]      
Useful life 20 years    
Building and improvements | Maximum      
Summary Of Significant Accounting Policies [Line Items]      
Useful life 50 years    
Land improvements | Minimum      
Summary Of Significant Accounting Policies [Line Items]      
Useful life 5 years    
Land improvements | Maximum      
Summary Of Significant Accounting Policies [Line Items]      
Useful life 20 years    
Special purpose entities      
Summary Of Significant Accounting Policies [Line Items]      
Net assets $ 2,780,000,000 2,950,000,000  
Net liabilities $ 2,630,000,000 $ 2,260,000,000