Inventories, Net and Significant Suppliers - Accounts Payable to Related Party Supplier (Details) - Related Party Supplier - Supplier Concentration Risk - Accounts Payable - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Accounts payable	$ 1,781	$ 1,500
Percent of accounts receivable, net	1.70%	1.30%