Summary of Significant Accounting Policies - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018
Accumulated Other Comprehensive Loss [Line Items]
Accumulated other comprehensive loss	$ (13,805)	$ (10,997)	$ (7,635)
AOCI Attributable to Parent
Accumulated Other Comprehensive Loss [Line Items]
Accumulated other comprehensive loss	(13,805)	(10,997)	(7,635)
Foreign currency translation adjustments
Accumulated Other Comprehensive Loss [Line Items]
Accumulated other comprehensive loss	(13,156)	(12,422)	(9,692)
Unrealized (losses) gains on interest rate swaps, net of tax
Accumulated Other Comprehensive Loss [Line Items]
Accumulated other comprehensive loss	$ (649)	$ 1,425	$ 2,057