Stockholders' Equity - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Total stock-based compensation expense	$ 22,349	$ 24,776	$ 46,773	$ 49,723
Curriculum and teaching
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Total stock-based compensation expense	49	17	96	33
Servicing and support
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Total stock-based compensation expense	4,321	3,964	8,680	7,813
Technology and content development
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Total stock-based compensation expense	2,635	3,095	6,497	6,369
Marketing and sales
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Total stock-based compensation expense	1,722	1,672	3,848	3,173
General and administrative
Stock-based compensation expense included in the unaudited condensed consolidated statements of operations
Total stock-based compensation expense	$ 13,622	$ 16,028	$ 27,652	$ 32,335