Significant Accounting Policies - Impact of Adoption on Balance Sheet (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Sep. 30, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting standards update	us-gaap:AccountingStandardsUpdate201613Member
Tuition receivable, net	$ 51,523	$ 45,958
Deferred income tax liabilities	47,942	34,012
Retained earnings	152,819	$ 188,392
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tuition receivable, net	51,523
Deferred income tax liabilities	47,942
Retained earnings	152,819
Cumulative Effect, Period of Adoption, Adjusted Balance | Revision of Prior Period, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tuition receivable, net	46,952
Deferred income tax liabilities	46,681
Retained earnings	149,509
Cumulative Effect Period of Adoption Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Tuition receivable, net	(4,571)
Deferred income tax liabilities	(1,261)
Retained earnings	$ (3,310)