Accounts Receivable - Company's Accounts Receivable and Securitized Accounts Receivable (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross receivables	$ 2,769,517	$ 2,371,778
Less allowance for doubtful accounts	(68,334)	(59,963)	$ (48,245)	$ (46,031)
Net accounts and securitized accounts receivable	2,701,183	2,311,815
Gross domestic accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross receivables	816,328	668,154
Gross domestic securitized accounts receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross receivables	974,000	886,000
Gross foreign receivables
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross receivables	$ 979,189	$ 817,624