Inventories - Valuation Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Inventory valuation allowance, beginning of the year	$ 9,801	$ 5,317
Inventory scrapped	(870)	(1,636)
Inventory utilized	(882)	(954)
Subtotal—usage	(1,752)	(2,590)
Write-downs of inventory valuation and transfers from other liabilities	14,967	7,074
Inventory valuation allowance, end of the year	$ 23,016	$ 9,801