Derivatives Notional Amounts - Designated as Hedges (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	$ 25,024	$ 14,620
Gain (Loss)	64	195
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	79,213	164,358
Unrealized Gain (Loss)	(691)	776
USD / AUD | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	4,341	5,841
Unrealized Gain (Loss)	16	316
USD / CAD | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	554	2,604
Unrealized Gain (Loss)	53	(18)
USD / CNY | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	954	11,252
Unrealized Gain (Loss)	17	(301)
USD / CHF | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	90	370
Unrealized Gain (Loss)	0	15
USD / EUR | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	42,200	60,387
Unrealized Gain (Loss)	(1,403)	1,826
USD / GBP | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	1,645	3,253
Unrealized Gain (Loss)	(22)	(75)
USD / NZD | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	6,930	9,650
Unrealized Gain (Loss)	67	(64)
USD / SEK | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	1,027	4,923
Unrealized Gain (Loss)	(112)	146
USD / MXP | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	1,517	6,148
Unrealized Gain (Loss)	142	(417)
EUR / AUD | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	139	506
Unrealized Gain (Loss)	3	6
EUR / GBP | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	12,184	14,511
Unrealized Gain (Loss)	398	(686)
EUR / NOK | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	7	0
Gain (Loss)	0	0
EUR / NOK | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	704	2,503
Unrealized Gain (Loss)	1	(25)
EUR / NZD | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	3,133	3,777
Unrealized Gain (Loss)	(9)	16
GBP / AUD | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	137	503
Unrealized Gain (Loss)	8	34
GBP / CHF | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	135	215
Unrealized Gain (Loss)	(1)	(10)
GBP / SEK | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	952	1,389
Unrealized Gain (Loss)	74	(42)
CHF / DKK | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	60	595
Unrealized Gain (Loss)	4	(2)
DKK / SEK | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	1,352	31,978
Unrealized Gain (Loss)	56	49
NOK / CHF | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	349	1,335
Unrealized Gain (Loss)	(23)	(13)
NOK / SEK | Designated as Hedging Instrument [Member]
Derivative [Line Items]
Notional Amount	810	2,618
Unrealized Gain (Loss)	$ 40	$ 21