Debt - Summary of Debt - Master Trust Notes (Details) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Debt Instrument [Line Items]    
Total debt, gross $ 4,100,348 $ 4,421,220
Debt discount, net (54,181) (51,586)
Deferred financing costs, net (41,183) (46,332)
Total debt, net 4,004,984 4,323,302
Master Trust Notes    
Debt Instrument [Line Items]    
Total debt, gross 1,696,766 1,710,380
Debt discount, net (23,919) (26,903)
Deferred financing costs, net (20,080) (22,113)
Total debt, net $ 1,652,767 1,661,364
Master Trust Notes | Series 2014-1 Class A1    
Debt Instrument [Line Items]    
Effective Interest Rates 6.00%  
Stated Rates 5.10%  
Remaining Term 4 years 8 months 12 days  
Total debt, gross $ 67,701 75,489
Master Trust Notes | Series 2014-1 Class A2    
Debt Instrument [Line Items]    
Effective Interest Rates 6.00%  
Stated Rates 5.40%  
Remaining Term 4 years 9 months 18 days  
Total debt, gross $ 253,300 253,300
Master Trust Notes | Series 2014-2    
Debt Instrument [Line Items]    
Effective Interest Rates 6.10%  
Stated Rates 5.80%  
Remaining Term 5 years 6 months  
Total debt, gross $ 230,490 232,867
Master Trust Notes | Series 2014-3    
Debt Instrument [Line Items]    
Effective Interest Rates 6.00%  
Stated Rates 5.70%  
Remaining Term 6 years 6 months  
Total debt, gross $ 312,385 312,705
Master Trust Notes | Series 2014-4 Class A1    
Debt Instrument [Line Items]    
Effective Interest Rates 3.90%  
Stated Rates 3.50%  
Remaining Term 4 years 3 months 18 days  
Total debt, gross $ 150,000 150,000
Master Trust Notes | Series 2014-4 Class A2    
Debt Instrument [Line Items]    
Effective Interest Rates 4.80%  
Stated Rates 4.60%  
Remaining Term 14 years 3 months 18 days  
Total debt, gross $ 360,000 360,000
Master Trust Notes | Total Master Trust 2014 notes    
Debt Instrument [Line Items]    
Effective Interest Rates 5.50%  
Stated Rates 5.10%  
Remaining Term 7 years 8 months 12 days  
Total debt, gross $ 1,373,876 1,384,361
Master Trust Notes | Series 2013-1 Class A    
Debt Instrument [Line Items]    
Effective Interest Rates 4.60%  
Stated Rates 3.90%  
Remaining Term 3 years 2 months 12 days  
Total debt, gross $ 125,000 125,000
Master Trust Notes | Series 2013-2 Class A    
Debt Instrument [Line Items]    
Effective Interest Rates 5.60%  
Stated Rates 5.30%  
Remaining Term 8 years 2 months 12 days  
Total debt, gross $ 197,890 201,019
Master Trust Notes | Total Master Trust 2013 notes    
Debt Instrument [Line Items]    
Effective Interest Rates 5.30%  
Stated Rates 4.70%  
Remaining Term 6 years 3 months 18 days  
Total debt, gross $ 322,890 $ 326,019