Intangible Assets - Summary of Future Amortization Expense (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Acquisition intangible assets, net, Net Carrying Amount	$ 10,357	$ 13,594
Capitalized Internal-Use Software, Net
Finite Lived Intangible Assets [Line Items]
Remainder of 2018	4,915
2019	11,243
2020	4,444
2021	70
2022	0
Acquisition intangible assets, net, Net Carrying Amount	20,672
Acquisition Intangible Assets, Net
Finite Lived Intangible Assets [Line Items]
Remainder of 2018	1,033
2019	3,839
2020	2,952
2021	1,705
2022	828
Acquisition intangible assets, net, Net Carrying Amount	$ 10,357