Summary of Significant Accounting Policies - Summary of Revenues Disaggregated by Type of Services (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	[1]
Disaggregation Of Revenue [Line Items]
Revenues	$ 86,766	$ 72,579
Promotion
Disaggregation Of Revenue [Line Items]
Revenues	63,783	57,319
Media
Disaggregation Of Revenue [Line Items]
Revenues	$ 22,983	$ 15,260

[1] As noted above, prior period amounts have not been adjusted under the modified retrospective method.