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Long Term Debt (Details) - USD ($)
12 Months Ended
Nov. 03, 2020
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Debt Instrument [Line Items]        
Cash and cash equivalents   $ 268,918,000 $ 187,509,000  
Revolving Credit Facility        
Debt Instrument [Line Items]        
Revolving credit facility, outstanding   141,600,000 141,800,000  
Interest paid   2,700,000 1,000,000 $ 500,000
Revolving Credit Facility | Australia, Dollars        
Debt Instrument [Line Items]        
Revolving credit facility, outstanding   $ 3,600,000 $ 3,800,000  
Revolving Credit Facility | Minimum        
Debt Instrument [Line Items]        
Margin rate 1.50%      
Unused commitment fee 0.20%      
Revolving Credit Facility | Maximum        
Debt Instrument [Line Items]        
Margin rate 2.00%      
Unused commitment fee 0.30%      
Amended Credit Facility | Revolving Credit Facility        
Debt Instrument [Line Items]        
Revolving credit facility, value $ 350,000,000      
Maximum aggregate incremental term loans $ 300,000,000      
Percentage of consolidated EBITDA to be funded 100.00%      
Maximum leverage ratio allowed in order to increase obligation 1.75      
Debt financing costs $ 1,900,000      
Debt instrument term 5 years      
Maximum total leverage ratio 2.00      
Cash and cash equivalents $ 150,000,000      
Minimum coverage ratio 1.75      
Minimum department of education financial composite score 1.0      
Minimum department of education financial composite score for two consecutive fiscal years 1.5      
Amendment to the Credit Facility, Subfacility for Borrowings in Foreign Currencies | Revolving Credit Facility        
Debt Instrument [Line Items]        
Revolving credit facility, value $ 150,000,000