Debt - Summary of Debt - Master Trust Notes (Details) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2015
Dec. 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
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 | Series 2014-1 Class A1    
Debt Instrument [Line Items]    
Effective Interest Rates 6.00%  
Stated Rates 5.10%  
Remaining Term 5 years  
Total debt, gross $ 70,336 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 5 years 1 month 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 8 months 18 days  
Total debt, gross $ 231,294 232,867
Master Trust Notes | Series 2014-3    
Debt Instrument [Line Items]    
Effective Interest Rates 6.00%  
Stated Rates 5.70%  
Remaining Term 6 years 8 months 18 days  
Total debt, gross $ 312,494 312,705
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 7 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 7 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 8 years  
Total debt, gross $ 1,377,424 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 6 months 18 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 6 months 18 days  
Total debt, gross $ 198,947 201,019
Master Trust Notes | Total Master Trust 2013 notes    
Debt Instrument [Line Items]    
Effective Interest Rates 5.20%  
Stated Rates 4.70%  
Remaining Term 6 years 6 months 18 days  
Total debt, gross $ 323,947 $ 326,019