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Derivative Financial Instruments - Fair Value of Derivative Instruments (Details) - Cash Flow Hedge - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest rate swap \| Other Current Assets [Member]
Derivative Liability
Derivative Asset	$ 127	$ 576
Interest rate swap \| Other Noncurrent Assets [Member]
Derivative Liability
Derivative Asset	0	369
Interest rate swap \| Other Noncurrent Liabilities [Member]
Derivative Liability
Derivative Liability	(498)	0
Foreign currency hedges \| Other Current Assets [Member]
Derivative Liability
Derivative Asset	395	393
Designated as Hedging Instrument [Member] \| Interest rate swap
Derivative Liability
Derivative Asset	(372)	945	$ 971
Designated as Hedging Instrument [Member] \| Foreign currency hedges
Derivatives, Fair Value [Line Items]
Foreign Currency Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months	432
Derivative Liability
Derivative Liability		$ 393	$ (742)
Derivative Asset	$ 395