Summary of Significant Accounting Policies - Narrative (Details)
 3 Months Ended 9 Months Ended
Jan. 01, 2020
USD ($)
Sep. 30, 2020
USD ($)
Sep. 30, 2019
USD ($)
Sep. 30, 2020
USD ($)
segment
Sep. 30, 2019
USD ($)
Dec. 31, 2019
USD ($)
Summary Of Significant Accounting Policies [Line Items]            
Net assets   $ 6,091,419,000   $ 6,091,419,000   $ 5,832,661,000
Net liabilities   2,759,238,000   $ 2,759,238,000   2,419,412,000
Number of segments | segment       1    
Rent escalators adjustment period       1 year    
Accounts receivable   28,500,000   $ 28,500,000   7,700,000
Accounts receivable, deemed not probable of collection   14,300,000   14,300,000   3,800,000
Deferred rental revenue receivables   89,300,000   89,300,000   83,600,000
Receivables, deemed not probable of collection   11,000,000.0   11,000,000.0   400,000
Goodwill impairment       0    
Income tax expense benefit   197,000 $ 11,190,000 406,000 $ 11,730,000  
Provision for income taxes       0    
Deferral rental income recognized CARES Act   $ 1,800,000   $ 24,100,000    
Deferred rent average repayment period       13 months    
Minimum            
Summary Of Significant Accounting Policies [Line Items]            
Rent deferral period       1 month    
Maximum            
Summary Of Significant Accounting Policies [Line Items]            
Rent deferral period       6 months    
Average            
Summary Of Significant Accounting Policies [Line Items]            
Rent deferral period       3 months    
SRAM            
Summary Of Significant Accounting Policies [Line Items]            
U.S. statutory federal income tax rate         21.00%  
Non-deductible executive compensation expenses         $ 700,000  
Net of federal income tax benefit         200,000  
Deferred income taxes and liabilities     0   0  
SRAM | Federal Income Tax            
Summary Of Significant Accounting Policies [Line Items]            
Income tax expense benefit     10,400,000   10,500,000  
SRAM | State Income Tax            
Summary Of Significant Accounting Policies [Line Items]            
Income tax expense benefit     $ 700,000   $ 700,000  
ASU 2017-04            
Summary Of Significant Accounting Policies [Line Items]            
Change in accounting principle, accounting standards update, adoption date   Jan. 01, 2020   Jan. 01, 2020    
Change in accounting principle, accounting standards update, adopted [true false]   true   true    
Accounting Standards Update 2016-13            
Summary Of Significant Accounting Policies [Line Items]            
Change in accounting principle, accounting standards update, adoption date   Jan. 01, 2020   Jan. 01, 2020    
Change in accounting principle, accounting standards update, adopted [true false]   true   true    
Recognition of loss due to adoption of new guidance $ 300,000          
Loans receivable and real estate assets held under direct financing lease $ 40,300,000          
Special Purpose Entity            
Summary Of Significant Accounting Policies [Line Items]            
Net assets   $ 350,400,000   $ 350,400,000   375,500,000
Net liabilities   $ 216,700,000   $ 216,700,000   $ 231,700,000