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Revenue recognition - Narrative (Details)
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2021
USD ($)
Jun. 30, 2020
USD ($)
Jun. 30, 2021
USD ($)
segment
Jun. 30, 2020
USD ($)
Dec. 31, 2020
USD ($)
Revenue from Contract with Customer [Abstract]          
Number of operating segments | segment     1    
Current portion of contract liabilities $ 54,500,000   $ 54,500,000   $ 44,600,000
Lessee, operating lease, remaining lease term 2 years   2 years    
Operating lease, lease income $ 16,900,000 $ 0 $ 35,600,000 $ 0  
Revenue, remaining performance obligation, amount 1,400,000,000   1,400,000,000    
Contract with customer, asset, noncurrent 39,700,000   39,700,000   41,100,000
Capitalized contract cost, amortization 1,600,000   1,600,000   0
Allowance for doubtful accounts receivable $ 3,400,000   $ 3,400,000   $ 3,100,000