Goodwill and Intangible Assets - Finite-lived and Indefinite-lived Intangibe Assets (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	61 months	57 months
Accumulated Amortization	$ (26,400)	$ (21,701)
Net Carrying Amount	24,213
Indefinite-lived trade name	3,600	3,600
Foreign currency translation adjustment	(185)	6
Total intangible assets, gross carrying amount	54,213	42,854
Intangible assets, net	$ 27,813	$ 21,153
Developed technologies
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	71 months	70 months
Gross Carrying Amount	$ 31,667	$ 20,657
Accumulated Amortization	(12,655)	(10,220)
Net Carrying Amount	$ 19,012	$ 10,437
Customer lists
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	47 months	47 months
Gross Carrying Amount	$ 9,970	$ 9,970
Accumulated Amortization	(6,505)	(5,480)
Net Carrying Amount	$ 3,465	$ 4,490
Trade names
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	44 months	46 months
Gross Carrying Amount	$ 6,113	$ 5,793
Accumulated Amortization	(4,542)	(3,465)
Net Carrying Amount	$ 1,571	$ 2,328
Non-compete agreements
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	31 months	30 months
Gross Carrying Amount	$ 2,018	$ 1,798
Accumulated Amortization	(1,668)	(1,506)
Net Carrying Amount	$ 350	$ 292
Master service agreements
Finite Lived Intangible Assets [Line Items]
Weighted-Average Amortization Period	21 months	21 months
Gross Carrying Amount	$ 1,030	$ 1,030
Accumulated Amortization	(1,030)	(1,030)
Net Carrying Amount	$ 0	$ 0