v3.20.4
Summary of significant accounting policies - Recent accounting pronouncements (Details) - USD ($)
$ in Thousands
12 Months Ended
Jan. 01, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Recent accounting pronouncements        
Accumulated deficit   $ 158,066 $ 140,973  
Property and equipment, net $ 406,328 406,328 380,243  
Long-term debt 171,695 171,695 162,708  
Income Tax Expense (Benefit)   157 (28) $ (5,153)
Additional paid-in capital 241,868 241,868 234,638  
Gross deferred tax liabilities   16,564 $ 19,651  
Convertible Notes        
Recent accounting pronouncements        
Gross deferred tax liabilities   $ 27,949    
ASU 2020-06 | Cumulative effect of a change in accounting principle        
Recent accounting pronouncements        
Property and equipment, net (6,076)      
Long-term debt 27,279      
Income Tax Expense (Benefit) 5,686      
Additional paid-in capital (39,921)      
ASU 2020-06 | Cumulative effect adjusted        
Recent accounting pronouncements        
Accumulated deficit 6,566      
Property and equipment, net 400,252      
Long-term debt 198,974      
Additional paid-in capital $ 201,947