Other Income (Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Component of Other Income (Expense), Nonoperating [Line Items]
Other income	$ 2,880	$ 2,351	$ 1,647
Gain (loss) on currency translation
Component of Other Income (Expense), Nonoperating [Line Items]
Other income	2,641	1,905	(293)
Hedge ineffectiveness
Component of Other Income (Expense), Nonoperating [Line Items]
Other income	218	(1,247)	(916)
Insurance recovery on furnace malfunction, net (see note 18)
Component of Other Income (Expense), Nonoperating [Line Items]
Other income	0	0	1,844
Other non-operating income
Component of Other Income (Expense), Nonoperating [Line Items]
Other income	$ 21	$ 1,693	$ 1,012