Derivatives - Forward Notional Contracts (Details) - Dec. 31, 2017 - Foreign currency forward contracts € in Thousands, ₩ in Thousands, ¥ in Thousands, ¥ in Thousands, £ in Thousands, SGD in Thousands, SFr in Thousands, SEK in Thousands, MXN in Thousands, HKD in Thousands, DKK in Thousands, CAD in Thousands, BRL in Thousands, AUD in Thousands	AUD	CNY (¥)	DKK	MXN	CHF (SFr)	KRW (₩)	GBP (£)	CAD	JPY (¥)	SGD	SEK	EUR (€)	HKD	BRL
Not designated as hedging instrument
Derivative [Line Items]
Notional amount of derivative	AUD 5,600	¥ 22,990	DKK 1,881	MXN 17,540	SFr 242	₩ 1,800,000	£ 1,868	CAD 2,076	¥ 178,500	SGD 5,023	SEK 4,775	€ 23,333	HKD 11,000	BRL 8,500
Derivatives designated as cash flow hedges | Designated as hedging instrument
Derivative [Line Items]
Notional amount of derivative		¥ 45,000	DKK 14,470	MXN 95,075	SFr 1,375		£ 3,625	CAD 2,310			SEK 16,330	€ 9,165