Summary of Significant Accounting Policies - Narrative (Details)
 3 Months Ended 9 Months Ended
Sep. 30, 2019
USD ($)
renewal_option
Sep. 30, 2018
USD ($)
Sep. 30, 2019
USD ($)
segment
renewal_option
Sep. 30, 2018
USD ($)
Jan. 01, 2019
USD ($)
Dec. 31, 2018
USD ($)
Summary Of Significant Accounting Policies [Line Items]            
Net assets $ 5,663,584,000   $ 5,663,584,000     $ 5,096,316,000
Net liabilities $ 2,330,804,000   $ 2,330,804,000     2,294,567,000
Number of segments | segment     1      
Number of renewal options (or more) | renewal_option 1   1      
Option to terminate, percentage (less than) 1.00%   1.00%      
Option to purchase, percentage (less than) 6.00%   6.00%      
Rent escalators adjustment period     1 year      
Reserves for uncollectible amounts $ 3,700,000   $ 3,700,000     4,900,000
Accounts receivable 10,000,000.0   10,000,000.0     12,400,000
Reserve for losses 700,000   700,000     1,100,000
Deferred rental revenue receivables 79,700,000   79,700,000     69,400,000
Goodwill impairment     0      
Federal income tax 11,190,000 $ 135,000 11,730,000 $ 475,000    
Provision for income taxes     0      
Bad debt expense 0   300,000      
Operating lease, right-of-use assets 5,600,000   5,600,000      
Operating lease, liabilities 7,675,000   7,675,000      
Accounting Standards Update 2016-02            
Summary Of Significant Accounting Policies [Line Items]            
Operating lease, right-of-use assets         $ 6,400,000  
Operating lease, liabilities         $ 8,600,000  
US Federal Income Tax            
Summary Of Significant Accounting Policies [Line Items]            
Federal income tax 10,402,000 51,000 10,500,000 64,000    
State Income Tax            
Summary Of Significant Accounting Policies [Line Items]            
Federal income tax $ 788,000 $ 84,000 $ 1,230,000 $ 411,000    
Walgreen Co.            
Summary Of Significant Accounting Policies [Line Items]            
Lease term 50 years   50 years      
Termination period     5 years      
Minimum            
Summary Of Significant Accounting Policies [Line Items]            
Renewal term 5 years   5 years      
Maximum            
Summary Of Significant Accounting Policies [Line Items]            
Renewal term 10 years   10 years      
Special Purpose Entity            
Summary Of Significant Accounting Policies [Line Items]            
Net assets $ 450,000,000   $ 450,000,000     900,000,000
Net liabilities 280,000,000   $ 280,000,000     $ 480,000,000
SRAM            
Summary Of Significant Accounting Policies [Line Items]            
U.S. statutory federal income tax rate     21.00%      
Non-deductible expense executive compensation     $ 700,000      
Net of federal income tax benefit     200,000      
Deferred income taxes and liabilities 0   0      
SRAM | US Federal Income Tax            
Summary Of Significant Accounting Policies [Line Items]            
Federal income tax 10,400,000   10,500,000      
SRAM | State Income Tax            
Summary Of Significant Accounting Policies [Line Items]            
Federal income tax $ 700,000   $ 700,000