Significant Accounting Policies -Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash included in other current assets	$ 13,287	$ 9,794
Minimum protective endowment held in an interest-bearing account	500	500
U.S. Higher Education
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash included in other current assets	1,400	700
Australia / New Zealand
Restricted Cash and Cash Equivalents Items [Line Items]
Restricted cash included in other current assets	11,900	$ 9,100
PENNSYLVANIA
Restricted Cash and Cash Equivalents Items [Line Items]
Minimum protective endowment held in an interest-bearing account	$ 500