Fair Value Measurements - Summary of Financial Liability Measured at Fair Value on a Recurring Basis (Details) - Designated As Hedging - Cash Flow Hedge - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Interest rate swap
Recurring financial liability that was measured at carrying value
Realized gain (loss) on cash flow hedge	$ 430	$ (421)
Derivative Asset	(372)	945	$ 971
Foreign currency hedges
Recurring financial liability that was measured at carrying value
Derivative liability		(393)	$ 742
Realized gain (loss) on cash flow hedge	624	484
Derivative Asset	395
Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap
Recurring financial liability that was measured at carrying value
Derivative liability	372	(945)
Recurring | Significant Other Observable Inputs (Level 2) | Foreign currency hedges
Recurring financial liability that was measured at carrying value
Derivative liability		(393)
Derivative Asset	395
Recurring | Carrying Value | Interest rate swap
Recurring financial liability that was measured at carrying value
Derivative liability	372	(945)
Recurring | Carrying Value | Foreign currency hedges
Recurring financial liability that was measured at carrying value
Derivative liability		$ (393)
Derivative Asset	$ 395