v3.26.3
Summary of significant accounting policies - Narrative (Details) - USD ($)
 3 Months Ended 9 Months Ended
Dec. 22, 2017
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2028
Jul. 01, 2027
Dec. 31, 2025
Summary of significant accounting policies              
Collateral account in connection with company's corporate card program     $ 2,800,000        
Restricted Cash, Noncurrent, Statement of Financial Position [Extensible Enumeration]     Deposits and Other Assets Noncurrent        
Allowance for credit loss   $ 0 $ 0 $ 0      
Allowance for doubtful accounts receivable     15,300,000       $ 15,200,000
Bad debt expense   $ 800,000 700,000 $ 8,600,000      
Income taxes              
Federal income tax statutory rate 21.00%            
Deposits and other assets              
Summary of significant accounting policies              
Bank guarantee denominated in foreign currency     700,000        
Hopewell Campus | Deposits and other assets              
Summary of significant accounting policies              
Letters of credit     3,000,000        
Warren Building under lease amendment              
Summary of significant accounting policies              
Letters of credit         $ 2,500,000 $ 5,000,000  
Warren Building under lease amendment | Deposits and other assets              
Summary of significant accounting policies              
Letters of credit     $ 10,000,000