Goodwill and Intangible Assets - Summary of Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Finite Lived Intangible Assets [Line Items]
Accumulated amortization	$ (11,399)	$ (4,696)
Total	35,145	6,262
Domain Names
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 1,268	1,268
Intangible assets, Average Remaining Useful Life	0 months
Trademarks
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 120	120
Intangible assets, Average Remaining Useful Life	0 months
Software
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 620	620
Intangible assets, Average Remaining Useful Life	5 months
Capitalized Learning Content
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 400	400
Intangible assets, Average Remaining Useful Life	25 months
Trade names
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 3,686	320
Intangible assets, Average Remaining Useful Life	32 months
Developed Technology
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 24,527	5,320
Intangible assets, Average Remaining Useful Life	44 months
Customer Relationships
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 15,923	$ 2,910
Intangible assets, Average Remaining Useful Life	32 months