Business acquisition - Assets Acquired and Liabilities Assumed (Details) - USD ($)
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Feb. 28, 2021
Nov. 27, 2020
Recognized amounts of identifiable assets acquired and liabilities assumed          
Amortization of intangible assets $ 2,322,000 $ 1,933,000 $ 0    
Goodwill 31,928,000 56,142,000 3,089,000    
Netless          
Business Combination, Consideration Transferred [Abstract]          
Cash     3,150,000    
Recognized amounts of identifiable assets acquired and liabilities assumed          
Cash and cash-equivalents     556,000    
Accounts receivable     203,000    
Prepayments and other current assets     24,000    
Contract asset     15,000    
Fixed assets     85,000    
Intangible assets, net     213,000    
Other non-current assets     850,000    
Salary and welfare payable     (31,000)    
Taxes payable and other accrued liabilities     (16,000)    
Deferred tax liabilities     (53,200)    
Total identifiable net assets acquired     911,000    
Goodwill     3,089,000    
Total purchase consideration     $ 4,000,000   $ 4,000,000.0
Deferred tax liability, period of recognition     5 years    
Finite-lived intangible asset, useful life     5 years    
Netless | General and Administrative Expense [Member] | Developed Technology [Member]          
Recognized amounts of identifiable assets acquired and liabilities assumed          
Amortization of intangible assets 42,600 42,600 $ 3,500    
Acquisition Of Easemob [Member]          
Business Combination, Consideration Transferred [Abstract]          
Cash   53,350,000      
Recognized amounts of identifiable assets acquired and liabilities assumed          
Cash and cash-equivalents   1,331,000      
Accounts receivable   451,000      
Prepayments and other current assets   704,000      
Contract asset   705,000      
Fixed assets   2,000      
Intangible assets, net   8,155,000      
Operating lease right-of-use assets   413,000      
Other non-current assets   26,000      
Accounts payable   (134,000)      
Advances from customers   (6,710,000)      
Salary and welfare payable   (2,863,000)      
Taxes payable and other accrued liabilities   (200,000)      
Operating lease liabilities   (363,000)      
Deferred tax liabilities   (1,219,000)      
Total identifiable net assets acquired   298,000      
Goodwill   53,052,000      
Total purchase consideration   $ 53,350,000   $ 53,400,000  
Acquisition Of Easemob [Member] | Developed Technology [Member]          
Recognized amounts of identifiable assets acquired and liabilities assumed          
Intangible assets, net $ 4,000,000.0        
Finite-lived intangible asset, useful life 5 years        
Acquisition Of Easemob [Member] | Accrued Expenses And Other Liabilities Current [Member]          
Recognized amounts of identifiable assets acquired and liabilities assumed          
Business Combination, Contingent Consideration, Liability, Current $ 4,600,000