Fair Value Measurements - Fair Value Inputs of Long-Lived Assets Held and Used (Details)
Sep. 30, 2019
ft²
$ / ft²
Dec. 31, 2018
ft²
$ / ft²
Fair Value Estimated Using Comparable Properties | Measurement Input, Price Per Square Foot | Retail    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input   0
Fair Value Estimated Using Comparable Properties | Measurement Input, Price Per Square Foot | Retail | Minimum    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input 34.45  
Fair Value Estimated Using Comparable Properties | Measurement Input, Price Per Square Foot | Retail | Maximum    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input 740.74  
Fair Value Estimated Using Comparable Properties | Measurement Input, Price Per Square Foot | Retail | Weighted Average    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input 76.17 0
Fair Value Estimated Using Comparable Properties | Measurement Input, Square Footage | Retail    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input | ft² 74,891 0
Fair Value Estimated Using Listing Price or Broker Opinion of Value | Measurement Input, Price Per Square Foot | Retail | Minimum    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input 30.14 185.42
Fair Value Estimated Using Listing Price or Broker Opinion of Value | Measurement Input, Price Per Square Foot | Retail | Maximum    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input 286.14 638.72
Fair Value Estimated Using Listing Price or Broker Opinion of Value | Measurement Input, Price Per Square Foot | Retail | Weighted Average    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input 44.90 507.11
Fair Value Estimated Using Listing Price or Broker Opinion of Value | Measurement Input, Price Per Square Foot | Office    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input 99.37 225.04
Fair Value Estimated Using Listing Price or Broker Opinion of Value | Measurement Input, Price Per Square Foot | Office | Weighted Average    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input 99.37 225.04
Fair Value Estimated Using Listing Price or Broker Opinion of Value | Measurement Input, Square Footage | Retail    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input | ft² 118,858 27,302
Fair Value Estimated Using Listing Price or Broker Opinion of Value | Measurement Input, Square Footage | Office    
Impaired Long-Lived Assets Held and Used [Line Items]    
Assets,measurement input | ft² 4,310 5,999