Significant Accounting Policies - Tuition Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Schedule of tuition receivable and allowance for doubtful accounts
Tuition receivable	$ 99,942	$ 82,454
Allowance for credit losses	(49,773)	(30,931)
Tuition receivable, net	50,169	51,523
Other assets
Schedule of tuition receivable and allowance for doubtful accounts
Tuition receivable, noncurrent	$ 3,600	$ 1,000