Debt (Details) - USD ($) | Feb. 08, 2019 | Mar. 31, 2019 | Feb. 07, 2019 | Feb. 06, 2019 | Dec. 31, 2018 |
Debt Instrument [Line Items] | | | | | |
Debt outstanding on facilities with fixed interest rates | | $ 4,484,600,000 | | | |
Debt Instrument Interest Rate During Period Fixed Rate Debt | | 4.26% | | | |
Long Term Debt, Percentage Bearing Fixed Interest Rate Remaining Term | | 3 years 9 months 26 days | | | |
Debt outstanding on facilities with interest rates based on floating rate indices | | $ 2,943,100,000 | | | |
Debt Instrument Interest Rate During Period Variable Rate Debt | | 4.22% | | | |
Long Term Debt, Percentage Bearing Variable Interest Rate Remaining Term | | 3 years 6 months 12 days | | | |
Percentage of Debt Hedged by Interest Rate Derivatives | | 84.00% | | | |
Debt Instrument Interest Rate During Period Fixed Rate and Interest Swap Rate Debt | | 4.17% | | | |
Hedged Portion of Debt Average Remaining Maturity | | 4 years 6 days | | | |
Debt Instrument, Interest Rate During Period | | 4.18% | | | |
Debt termination expense | | $ 0 | | | |
Institutional Notes [Domain] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt and Capital Lease Obligations | | $ 2,167,257,000 | | | $ 2,198,200,000 |
Debt Instrument, Interest Rate, Effective Percentage | | 4.73% | | | |
Asset-backed securitization term notes | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt and Capital Lease Obligations | | $ 2,967,601,000 | | | 3,063,821,000 |
Debt Instrument, Interest Rate, Effective Percentage | | 3.95% | | | |
Term Notes [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Interest Rate, Effective Percentage | | 4.06% | | | |
Asset Backed Warehouse Facility [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt and Capital Lease Obligations | | $ 350,000,000 | | | 340,000,000 |
Debt Instrument, Advance Rate Used in Calculating Borrowing Capacity | | 81.00% | | | |
Debt Instrument, Interest Rate, Effective Percentage | | 4.24% | | | |
Maximum borrowing capacity | | $ 1,200,000,000 | | | |
Line of Credit Facility, Remaining Borrowing Capacity | | 400,000,000 | | | |
Revolving credit facilities | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt and Capital Lease Obligations | | $ 365,000,000 | | | 375,000,000 |
Debt Instrument, Advance Rate Used in Calculating Borrowing Capacity | | 83.00% | | | |
Debt Instrument, Interest Rate, Effective Percentage | | 4.49% | | | |
Maximum borrowing capacity | | $ 1,235,000,000 | $ 300,000,000 | $ 800,000,000 | |
Capital lease obligations | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt and Capital Lease Obligations | | 73,399,000 | | | $ 75,526,000 |
Interest Rate Swap [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Net notional amount | | $ 1,753,300,000 | | | |
Net Notional Amount of Interest Rate During Period | | 2.24% | | | |
Weighted Average Remaining Term | | 4 years 5 months 7 days | | | |
Minimum [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Capital Lease Period Over Which Interest Expense Recognized Preceding Early Purchase Option | | 3 years | | | |
Minimum [Member] | Institutional Notes [Domain] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Term | | 7 years | | | |
Debt Instrument, Advance Rate Used in Calculating Borrowing Capacity | | 83.00% | | | |
Minimum [Member] | Asset-backed securitization term notes | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Advance Rate Used in Calculating Borrowing Capacity | | 77.00% | | | |
Minimum [Member] | Term Notes [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Advance Rate Used in Calculating Borrowing Capacity | | 79.00% | | | |
Minimum [Member] | Asset Backed Warehouse Facility [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Bank Account Maintenance Required Amount Balance, Interest Expense | | 3 months | | | |
Minimum [Member] | Capital lease obligations | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Interest Rate, Effective Percentage | | 3.60% | | | |
Maximum [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Capital Lease Period Over Which Interest Expense Recognized Preceding Early Purchase Option | | 10 years | | | |
Maximum [Member] | Institutional Notes [Domain] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Term | | 12 years | | | |
Debt Instrument, Advance Rate Used in Calculating Borrowing Capacity | | 85.00% | | | |
Maximum [Member] | Asset-backed securitization term notes | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Advance Rate Used in Calculating Borrowing Capacity | | 87.00% | | | |
Maximum [Member] | Term Notes [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Advance Rate Used in Calculating Borrowing Capacity | | 83.00% | | | |
Maximum [Member] | Capital lease obligations | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Interest Rate, Effective Percentage | | 4.93% | | | |
London Interbank Offered Rate (LIBOR) [Member] | Asset Backed Warehouse Facility [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Basis Spread on Variable Rate | 1.75% | | | | |
Pre-Conversion [Member] | London Interbank Offered Rate (LIBOR) [Member] | Asset Backed Warehouse Facility [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Basis Spread on Variable Rate | 2.85% | 1.85% | | | |
Post-Conversion [Member] | London Interbank Offered Rate (LIBOR) [Member] | Asset Backed Warehouse Facility [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument, Basis Spread on Variable Rate | | 2.85% | | | |
Interest Rate Swap [Member] | | | | | |
Debt Instrument [Line Items] | | | | | |
Debt Instrument Interest Rate During Period Variable Rate Debt | | 4.06% | | | |
Debt and Capital Lease Obligations | | $ 6,237,900,000 | | | |