Derivatives Derivative Financial Instruments - Naratives (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2012 USD ($) item	Jun. 24, 2012 USD ($) item
Derivative [Line Items]
Unrealized Loss on Foreign Currency Derivatives, before Tax	$ 683
Derivative Asset	97
Foreign Currency Cash Flow Hedge Liability at Fair Value	839
Designated as Hedging Instrument | Interest Rate Swap
Derivative [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months	(278)
Cash Flow Hedge | Designated as Hedging Instrument | Foreign currency hedges
Derivative [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months	567
Derivative, Notional Amount	33,200
Interest rate swap - cash flow hedge	$ 742		$ 601	$ 0
Cash Flow Hedge | Designated as Hedging Instrument | Interest Rate Swap
Derivative [Line Items]
Derivative, Notional Amount		$ 50,000			$ 25,000	$ 50,000
Derivative, Number of Instruments Held | item		3			4	4
Interest rate swap - cash flow hedge			$ (753)	$ 768