Derivatives Notional Amounts - Not Designated as Hedges (Details) - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Derivative [Line Items]
Notional Amount	$ 30,963		$ 25,318
Gain (Loss)	(12)		219
Forward exchange contracts—net
Derivative [Line Items]
Gain (Loss)	(12)	$ 230
AUD / USD
Derivative [Line Items]
Notional Amount	5,200		11,500
Gain (Loss)	12		167
CAD / USD
Derivative [Line Items]
Notional Amount	15,037		0
Gain (Loss)	(30)		0
EUR / USD
Derivative [Line Items]
Notional Amount	1,026		0
Gain (Loss)	8		0
NZD / USD
Derivative [Line Items]
Notional Amount	3,700		3,000
Gain (Loss)	23		30
AUD / NZD
Derivative [Line Items]
Notional Amount	6,000		10,800
Gain (Loss)	(25)		22
EUR / NOK
Derivative [Line Items]
Notional Amount	0		18
Gain (Loss)	$ 0		$ 0