Debt - ABL Credit Facility & Other Borrowings (Details) - USD ($)	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Remaining Capacity	$ 546,700,000
Availability Under Borrowing Base Limitation	546,700,000
Line of Credit | ABL Credit Facility | Senior Secured Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,750,000,000
Debt, gross	1,177,800,000	$ 1,130,000,000
Remaining Capacity	546,700,000
Availability Under Borrowing Base Limitation	546,700,000
Line of Credit | ABL Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	350,000,000
Line of Credit | ABL Credit Facility | Letter of Credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	250,000,000
Remaining Capacity	224,500,000
Letter of credit outstanding	25,500,000
Long-term Line of Credit	0
Line of Credit | Other borrowings
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 10,000,000
Line of credit facility, percentage ratio of interest rate to prevailing base lending rates	110.00%
Debt, gross	$ 6,300,000	2,600,000
Remaining Capacity	3,700,000
Line of Credit | Asset-backed Securities, Securitized Loans and Receivables [Member]
Line of Credit Facility [Line Items]
Debt, gross	175,000,000	$ 0
Remaining Capacity	0
Availability Under Borrowing Base Limitation	$ 0