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	6 Months Ended	12 Months Ended
	Jun. 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	$ 313	$ (421)
Derivative Asset	252	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	315	484
Derivative Asset	718
Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swap
Recurring financial liability that was measured at carrying value
Derivative liability	(252)	(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	718
Recurring | Carrying Value | Interest rate swap
Recurring financial liability that was measured at carrying value
Derivative liability	(252)	(945)
Recurring | Carrying Value | Foreign currency hedges
Recurring financial liability that was measured at carrying value
Derivative liability		$ (393)
Derivative Asset	$ 718