Summary of Significant Accounting Policies - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Accumulated Other Comprehensive Loss [Line Items]
Accumulated other comprehensive loss	$ (9,087)	$ (14,019)	$ (21,602)
AOCI Attributable to Parent
Accumulated Other Comprehensive Loss [Line Items]
Accumulated other comprehensive loss	(9,087)	(14,019)	(21,602)
Foreign currency translation adjustments
Accumulated Other Comprehensive Loss [Line Items]
Accumulated other comprehensive loss	(8,437)	(4,917)	(10,447)
Unrealized (losses) gains on interest rate swaps, net of tax
Accumulated Other Comprehensive Loss [Line Items]
Accumulated other comprehensive loss	$ (650)	$ (9,102)	$ (11,155)