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Related Party Transactions (Details)
12 Months Ended
Dec. 31, 2019
USD ($)
ft²
property
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Related Party Transaction [Line Items]      
Revenue from leases $ 296,142,000 $ 317,783,000 $ 403,635,000
Mack [Member]      
Related Party Transaction [Line Items]      
Due from related parties 0 0  
Marshall [Member]      
Related Party Transaction [Line Items]      
Due to Related Parties, Current 120,000 148,000  
Accounts Payable, Related Parties, Current 0 0  
RG [Member]      
Related Party Transaction [Line Items]      
Related party revenue $ 674,000 1,114,000 1,873,000
Leased Office Space 1 [Member] | Mack [Member]      
Related Party Transaction [Line Items]      
Area Of Real Estate Property | ft² 5,930    
Number of real estate properties | property 1    
Lease expiration date January 2025    
Previously Leased [Member]      
Related Party Transaction [Line Items]      
Number of real estate properties | property 1    
Previously Leased [Member] | Mack [Member]      
Related Party Transaction [Line Items]      
Area Of Real Estate Property | ft² 7,034    
Revenue from leases $ 18,000 $ 193,000 $ 187,000