Debt - Summary of Debt (Details) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2015
Dec. 31, 2014
May. 31, 2014
Debt Instrument [Line Items]      
Total debt, gross $ 4,092,862 $ 4,421,220  
Debt discount, net (54,247) (51,586)  
Deferred financing costs, net (42,870) (46,332)  
Total debt, net $ 3,995,745 4,323,302  
Weighted Average      
Debt Instrument [Line Items]      
Weighted Average Effective Interest Rates 5.33%    
Weighted Average Stated Rates 5.00%    
Weighted Average Term 5 years 3 months 18 days    
Revolving Credit Facilities      
Debt Instrument [Line Items]      
Total debt, gross $ 20,000 15,181  
Revolving Credit Facilities | Weighted Average      
Debt Instrument [Line Items]      
Weighted Average Stated Rates 1.89%    
Weighted Average Term 3 years 9 months 18 days    
Master Trust Notes      
Debt Instrument [Line Items]      
Total debt, gross $ 1,701,371 1,710,380  
Debt discount, net (24,921) (26,903)  
Deferred financing costs, net (20,809) (22,113)  
Total debt, net $ 1,655,641 1,661,364  
Master Trust Notes | Weighted Average      
Debt Instrument [Line Items]      
Weighted Average Effective Interest Rates 5.44%    
Weighted Average Stated Rates 5.04%    
Weighted Average Term 7 years 8 months 18 days    
CMBS - fixed-rate      
Debt Instrument [Line Items]      
Total debt, gross $ 1,554,414 1,836,181  
CMBS - fixed-rate | Weighted Average      
Debt Instrument [Line Items]      
Weighted Average Effective Interest Rates 5.45%    
Weighted Average Stated Rates 5.88%    
Weighted Average Term 2 years 10 months 18 days    
CMBS - variable-rate      
Debt Instrument [Line Items]      
Total debt, gross $ 68,345 110,685  
CMBS - variable-rate | Weighted Average      
Debt Instrument [Line Items]      
Weighted Average Effective Interest Rates 3.42%    
Weighted Average Stated Rates 3.55%    
Weighted Average Term 3 years 2 months 18 days    
Convertible Notes      
Debt Instrument [Line Items]      
Total debt, gross $ 747,500 747,500  
Deferred financing costs, net     $ (19,600)
Convertible Notes | Weighted Average      
Debt Instrument [Line Items]      
Weighted Average Effective Interest Rates 4.86%    
Weighted Average Stated Rates 3.28%    
Weighted Average Term 4 years 9 months 18 days    
Unsecured fixed rate promissory note      
Debt Instrument [Line Items]      
Total debt, gross $ 1,232 $ 1,293  
Unsecured fixed rate promissory note | Weighted Average      
Debt Instrument [Line Items]      
Weighted Average Effective Interest Rates 9.12%    
Weighted Average Stated Rates 7.00%    
Weighted Average Term 6 years 6 months 18 days