Accounts Receivable - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Accounts receivable, allowances for doubtful accounts	$ 23,400		$ 22,400	$ 23,400	$ 22,400	$ 25,400
Bad debt expense				43,617	11,758
MAT Sales Reversal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net sales reversal		$ 30,000	43,000		43,000
Bad debt expense	(13,000)			37,000
Accounts receivable reversal	$ 13,000	$ 30,000	$ 47,000	$ 67,000	$ 47,000