Equity Investments in Real Estate - Narratives (Details) - USD ($)
 1 Months Ended 12 Months Ended
Feb. 28, 2017
Feb. 01, 2017
Oct. 26, 2016
Jul. 29, 2016
Apr. 11, 2016
Jan. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Schedule of Equity Method Investments                    
Impairment charges             $ 29,706,000 $ 1,023,000 $ 570,000  
Goodwill impairment             0      
Equity in earnings of equity method investments in real estate             3,262,000 14,667,000 24,073,000  
Proceeds from mortgage financing             266,970,000 170,233,000 92,791,000  
Repayments of secured debt             177,469,000 121,267,000 51,309,000  
Non-recourse mortgage loans             $ 170,900,000 $ 170,200,000    
Debt Instrument, Term             7 years 1 month 6 days 8 years 7 months 6 days    
Preferred return             5.00%      
Proceeds from equity method investment             $ 42,744,000 $ 34,962,000 83,882,000  
Unamortized basis differences on our equity investments             19,100,000 26,500,000    
Equity Method Investments                    
Schedule of Equity Method Investments                    
Equity in earnings of equity method investments in real estate             9,867,000 18,227,000 28,348,000  
Unconsolidated Equity Investments                    
Schedule of Equity Method Investments                    
Proceeds from equity method investment             $ 57,800,000 52,100,000 28,700,000  
Minimum                    
Schedule of Equity Method Investments                    
Ownership interest, percentage             7.00%      
Maximum                    
Schedule of Equity Method Investments                    
Ownership interest, percentage             97.00%      
Subsequent Event                    
Schedule of Equity Method Investments                    
Repayments of secured debt $ 42,900,000 $ 92,400,000                
Non-recourse mortgage loans   $ 105,000,000                
Net Lease | Equity Method Investments                    
Schedule of Equity Method Investments                    
Impairment charges             $ 1,900,000   800,000  
Equity in earnings of equity method investments in real estate             15,271,000 21,692,000 12,571,000  
Self storage | Equity Method Investments                    
Schedule of Equity Method Investments                    
Equity in earnings of equity method investments in real estate             (394,000) (1,703,000) (1,878,000)  
All Other | Equity Method Investments                    
Schedule of Equity Method Investments                    
Equity in earnings of equity method investments in real estate             (5,010,000) $ (1,762,000) $ 17,655,000  
C1000 Logistiek Vastgooed B.V | Net Lease                    
Schedule of Equity Method Investments                    
Mortgage debt on tenancy in common             58,100,000      
C1000 Logistiek Vastgooed B.V | WPC | Net Lease                    
Schedule of Equity Method Investments                    
Mortgage debt on tenancy in common             $ 68,400,000      
Ownership interest, percentage             85.00%      
Tesco plc | Net Lease                    
Schedule of Equity Method Investments                    
Non-recourse mortgage loans       $ 17,000,000            
Tesco plc | WPC | Net Lease                    
Schedule of Equity Method Investments                    
Repayments of secured debt       33,800,000            
Non-recourse mortgage loans       $ 34,600,000            
Interest rate on debt       5.90%            
Debt Instrument, Term       5 years            
Ownership interest, percentage             49.00%      
Tesco plc | EURIBOR | WPC | Net Lease                    
Schedule of Equity Method Investments                    
Interest rate on debt       3.30%            
Madison Storage NYC, LLC and Veritas Group IX-NYC, LLC | Self storage                    
Schedule of Equity Method Investments                    
Ownership interest, percentage         100.00%     45.00%   45.00%
Indirect ownership interest in equity investments               40.00%   40.00%
Increase in ownership equity investments     40.00%   15.00%          
Shelborne Property Associates, LLC | All Other | Third Party                    
Schedule of Equity Method Investments                    
Goodwill impairment             $ 22,800,000      
Contract termination income             10,600,000      
Guaranteed loss compensation             $ 10,600,000      
Ownership interest, percentage             33.00%      
Hellweg 2                    
Schedule of Equity Method Investments                    
Equity in earnings of equity method investments in real estate               $ 6,200,000    
Hellweg 2 | Net Lease | Subsequent Event                    
Schedule of Equity Method Investments                    
Proceeds from mortgage financing           $ 89,000,000        
Hellweg 2 | WPC | Net Lease                    
Schedule of Equity Method Investments                    
Ownership interest, percentage             37.00%      
Hellweg 2 | WPC | Net Lease | Subsequent Event                    
Schedule of Equity Method Investments                    
Proceeds from mortgage financing           $ 243,800,000        
BPS Nevada, LLC | Net Lease                    
Schedule of Equity Method Investments                    
Preferred return             12.00%      
BPS Nevada, LLC | Net Lease | Minimum                    
Schedule of Equity Method Investments                    
Preferred return               8.00%    
BPS Nevada, LLC | Net Lease | Maximum                    
Schedule of Equity Method Investments                    
Preferred return               12.00%    
BPS Nevada, LLC | Net Lease | Third Party                    
Schedule of Equity Method Investments                    
Ownership interest, percentage             15.00%