Schedule II—Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for doubtful trade receivables
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 5,570	$ 7,739	$ 6,241
Charges to costs and expenses	1,709	1,259	5,741
Recoveries and write offs	(2,760)	(3,428)	(4,243)
Balance at end of period	4,519	5,570	7,739
Allowance for excess and slow moving inventory
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	45,648	39,247	34,607
Charges to costs and expenses	32,204	5,748	8,512
Recoveries and write offs	5,714	653	(3,872)
Balance at end of period	$ 83,566	$ 45,648	$ 39,247